I've done a short scenario for Richard of York as king after Henry VI, on the same premise that he was not killed at Wakefield, in my published 'Alternative History of Britain: The Wars of the Roses' ( Tim Venning, pub. Pen and Sword, 2013) , and have some further ideas on this basis lined up for Sealion later on. One of the crucial points here is that, as suggested above , Edward of York (E IV) would not have dared to secretly marry Elizabeth Woodville had his father still been alive as of 1464; he would presumably have been married off to Louis XI of France's wife's sister Bona of Savoy, as his cousin Warwick wanted in OTL to establish an Anglo-French rapprochement. Alternatively, if we have a slightly different arc to events in Castile, King Henry of C could have pressed more determinedly for Edward to be married to his half-sister Isabella (Queen of C after Henry in OTL) to get her out of the country to improve the chances of his daughter, Juana 'la Beltraneja', succeeding him. That way, if Isabella (born 1451) marries Edward (born April 1442) in the mid-1460s, when Isabella's full brother Alfonso dies in 1468 there is no candidate for Juana's enemies to back in the succession to Henry in 1473-4 and his choice Juana succeeds as Queen; Isabella is not in Spain to marry Ferdinand of Aragon so the two kingdoms are not united. The fanatically devout and competent Isabella and the promiscuous and sporadically lazy, worldly Edward would have made an interesting pair on the English throne - but if the marriage had worked Isabella could have been as forceful a Queen as Margaret of Anjou. Given her passion for converting 'heretics' and backing religious orders and the lack of serious religious dissidence in England (Jews expelled 1290, a few Lollards), would she have put her energies into reviving devotion in the monasteries with up to date new Orders - meaning less excuse for a C16th English King to abolish them - or backed Columbus in 1492 and established an English mercantile base on Cuba or Hispaniola? (The English had far fewer potential colonists than Spain did.) The poorer resourced English would have been likelier to trade with than try to conquer and settle Mexico, unless they had a long-term ally in Castile to provide more men. How about an Anglo-Castilian expedition c. 1519 to aid the subject peoples of the Aztecs , eg the Tlascalans, overthrow Mocteczuma in return for trade concessions and loot, but the still divided Spanish kingdoms devoting most of their energy to North Africa?
Assuming that Richard of York (born 1411) avoids Somerset's army in Dec 1460 by fleeing Sandal Castle and not being caught there, or does not even go to Yorkshire to raise troops but sends his brotherin law Salisbury instead, his second son Edmund of Rutland (born 1443)is unlikely to be at Sandal either to be killed in the battle at Wakefield. That way, he not Clarence is the next heir if Edward has no sons , and presumably he will have some foreign princess chosen for him by his father and Warwick. (Or would Warwick try to marry him off to his elder daughter Isabel, Clarence's wife in OTL?) So if Richard dies some time around 1470 to 1475 and Edward is King but with only daughters (Isabella had one son in real life but he died young), we do not have the threat of Clarence as the next King if he can dispossess Edward's children, and probably Edward's marriage is above board and undeniably legal. Richard of Gloucester
never gets near the throne and can devote himself to warfare, either against Scotland or France, as allowed by his brother Edward, and can possibly be used by Edward to secure control of Brittany in the 1480s - and as his ailing first wife Anne Neville dies he can be married off to the Breton heiress Anne and installed as Duke of Brittany to annoy the French. The House of York stays on the throne.
At most, if Edward has only daughters there's a feud over who will marry them and be King Consort -
Edmund's son, or Clarence's son? Presumably the Yorkists defeat Margaret of Anjou in early 1461 and she ends up fleeing to Scotland as in OTL, and Henry VI is never rescued by her forces as in OTL so he stays in the Tower until disposed of on the quiet. The Tudors do not stand a chance of the throne, unless Edmund of Rutland is as unstable and greedy as Clarence and Richard III in OTL and one of those two starts a civil war against Edward IV's heirs. But if Edward does die young (in his forties?) due to drink, over-eating or whatever, a loyal Edmund as regent or a competent and ruthless Queen Mother Isabella are quite capable of seeing off Clarence or Richard.
