There was a place the French kept but in Tunisia and it was a naval base at Bizerte.
This is how it went on. Clear victory on the ground for the French and two years later, the Tunisians got them to leave just like they wanted in the first place.
Militarily, Oran can be probably be held on to, but what's the point, really, and soon the political will vanish.
The OAS were at least one order of magnitude worse than any side in the Troubles, in the brief time they operated, I think, and they did not even have to go to the Americans for heavy weapons. If they have a 'dream' they can still hold on to part of Algeria they'll fight to the bitter end.
And anyway, the strength of the pieds-noirs came from all the land their ancestors had stolen from the Algerians. It was the fertile land, it was the land best connected to the distribution network, etc. Apart from the minority of Oranian shopkeepers already there, how are we to cram one million people in a single sort of city-state without any farming hinterland, shorn of all their wealth?