That was a lot of background there, but
what if René Goscinny lived up to the late 2010's/early 2020's as Tchernia, Tabary or Uderzo?
(partly based on this article :
https://www.marianne.net/agora/et-si-rene-goscinny-netait-pas-mort-a-51-ans)
When it comes to comics, I think that Goscinny will continue his gradual withdrawal. While not outright giving up on this career, he already slowed down his production IOTL adopting a more "Hergian" rythm instead of writing several scenarii per year as he was used to.
You'd probably see something like one Astérix album every two or three years : how it could go however is not something easy to clear out. I don't think he was any less interested on the character, but his outlook did change with years as Uderzo's did, fearful of giving room to critics accusing him of doing the same formula over and over again.
We might see either a (very relatively) "darker" moral satirism comparable to Iznogoud tackling more about modern French society (as Le Domaine des Dieux ou La Zizanie did, but a bit "meaner", reflecting Goscinny own reaction, maybe?), or conversely a more fantastical and more character-heavy take comparable to Uderzo's own works IOTL.
In fact, we could very well seeing both following each other, if Goscinny's involvement in animation and cinema is successful and demanding enough, with the possiblity of Uderzo trying his hand on short Asterix stories to "make it up" for more wait between albums before eventually becoming sole authors of some Asterix long stories as IOTL with the difference collaboration with Goscinny and more gradual training would probably lead to better critical reception.
Instead of an alternance of each album being "Gauls going abroad" or "Gauls dealing with a crisis at home", we might thus see a more stylistic switch between "Gauls satirize aspects of modern society" (likely at home or among themselves) and "Gauls go on a grand trip around" (abroad or, maybe, in folklore), maybe ending as proposed by the article with a more "classical"
Asterix and the Vascons as a closure of a series going full circle.
Morris having renewed the contract on Lucky Luke on Goscinny's back, I could see the latter being quite bitter about it and deciding to stop further collaboration on the series at least for the time being : as far as he was concerned, it was an hurtful betrayal from one of his older collaborators (actually going further back than Astérix), and I wouldn't think that he would readily forgive that. That would pretty mean the same thing as IOTL, Morris being uninterested on writing Lucky Luke as he did early on and going with younger scenarists with an immediate drop in critical quality.
I can see Goscinny collaborating still on Iznogoud, as he had an a priori excellent work relation with Tabary (who would probably follow him in breaking with Dargaud), but possibly giving him more leeway on scenario-making on the same grounds as it could happen ITTL with Uderzo, especially giving Tabary kept producing scenarii IOTL and was intent on continuing the series after Goscinny's death.
While Goscinny's death in 1977 pretty much put a stop to personal criticism on his character, with a rehabilitation from both renowed colleagues (
as Franquin) and most of the youngs authors that heavily criticized him, and while I could still see a lot of these people bent on defending René Goscinny's influence on comics, I definitely think you"d have a much more long lasting scorn from both more radical, fashionable or modern authors as well as part of the BD cultural establishment willing to preserve a distance between "serious" and "popular" comics, maybe up to promoting and settling a distinction comparable to IOTL American "comics"/"graphic novel" with "bande dessinée/roman graphique" (which tbh, exist IOTL in bande dessinée but also appears as much more snobbish).
Eventually,
films and especially animated movies are likely to be the main focus of a longer-living Goscinny from this point on. Assuming the legal conflict between Uderzo (with Goscinny here) and Dargaud unfolds as IOTL, he would still keep movie adaptation rights to his comics, fueling a comparable endeavour and influence he had in Franco-Belgian comics in French animation.
IOTL, Iznogoud was being planned to be adapted by Studio Idéfix as a live-action movie with Louis De Funès : but as he refused, I don't think you'd have much momentum to actually adapt it as such and maybe more probably so as an animated movie with reduced ambitions (being a less popular character and without star-effect bought by De Funès).
In fact, while Goscinny did have some successes along with disappointments in live-action movies, I think Studio Idéfix would remain essentially an animation studio except maybe producing small movies if they have the funds for.
As the article proposes, I could see Goscinny being also willing to create his own animated character and series with this
Baron de l'Etiquette as a Saint-Simonian satire of Louis XIV court, maybe as a direct-to-TV series rather than as a theatrical movie, as he seem to have more comfortable with a sketch structure when it came to long stories (You just have to look at the Twelve Tasks of Asterix and Ballad of Daltons) which don't really gives as much in movie format as it does in serial comics.
On the other hand, I could see him acting as a mentor of sort to authors willing to adapt their stories, either from comics or from novels, as to make them more accessible to the general public. I'd see a specific approach from someone that was still essentially marked by his editorial career, and less prone to force in a specific studio style especially since it wouldn't be as person-centered as were Don Bluth or Myasaki studios.
It's really harder to speculate about what could have been done there, besides adaptation of Goscinny's own work (safe Lucky Luke ITTL) like Asterix, Iznogoud (maybe just a one-time event IMO), Le Petit Nicolas or from comics or works he had affinities with the authors : there we could see an actual Barbe-Rouge movie adaptation (maybe of the Aztec Treasure arc?), Tanguy et Laverdure (possibly as an actual political live-action movie as it would be much easier to have the props and authorisation), Valérian et Laureline, etc.
Dreaming there a bit, imagine what could have be made with "Il était une fois...l'espace" with an actual budget, skills, time, etc. turning it as an actual domestic equivalent of Star Trek for a generation.
Assuming a steady enough income from royalties and theaters entrances, you might have avoided the animation "gap" of the 80's in France, both when it comes to its public perception (still pretty much "familial") and accessibility of skills : ITTL, continuity of presence of "old" specialists and incoming generation along with some cultural protectionism would allow animated movies within (and eventually outside) Studio Idéfix to have an overall better quality.
Not something comparable in scale to Disney (maybe more akin to Don Bluth on this regard), but allowing people like Laloux to produce domestically without going for Hungarian or North Korean taskforce. You might see movies like
Gandahar being up to their writing and ambitions instead of...you know, cult-following like appreciation and more likely to be sold abroad : not something even making a dent at Disney or American studios both abroad or in Europe of course, but possibly creating a strong domestic and European market alongside.
I don't think it would be nearly enough to "stop" or change much about the influence of Japanese animation in France, altough possibly pushing for more actual collaboration as with Ulysses 31, and I actually would see Studio Idéfix being uneasy or even uninterested to the idea incorporating it (if later IOTL Uderzo take on manga is any indication, but he was admittedly old and quite bitter at this point). However, what could change ITTL is that promotion and presence of accessible domestic animation studios might led to a much lesser presence of Japanimation in France : IOTL, TF1 channel imported them by the ton which made France a prime market for Japanese animation and comics (actually the main market outside Japan). ITTL, altough unlikely to be comparable to how delayed it was in USA. It could however be an additional reason for Studio Idédix to be retiscent to this and actually lobbying.
Likewise I wouldn't be surprised that Studio Idéfix would completely pass away from video-games applications.
What happens after the 90's is IMO too hard to propose, giving it changes gradually a lot of stuff in domestic and european perception of animation, what makes it popular, which themes are around, etc. But if it wouldn't be unthinkable to propose Studio Idéfix becoming interested on develloping techniques notably computer animation, I don't think they would have a leading role there.
Overall when it comes to their influence, I would think Goscinny would have a comparable one he had in comics : acting as a facilitator, someone shifting the general public perception about animation as being a mature media on its own, using profits from Asterix and Studio Idéfix movies to first lead on some domestic adaptations, and eventually trough creating the structures and the means for governmental subsides (which would be *the* financial distinction of French animation ITTL as well compared to American and Japanese) earlier ITTL.