@calvin1417
We might just need a reason for *Henry VI to marry Eleanor of Aquitaine : I know pre-1900 can tend to be some kind of wild match-making sub-forum, but there's no real geopolitical or diplomatical reason to do so. The union with Louis VII was basically a way to prevent the desintegration of the duchy, by having its suzerain's resources (and authority) at disposal, something that *Henry VI obviously couldn't.
Eventually, in a situation where the House of Blois secures the english throne, you might see (if Louis still repudiates Aliénor ITTL) an union with Thibault rather than Henri for the same reasons.
Heh. While Guillaume may have a fair chance to take over Normandy proper (especially with Capetian support as he recieved IOTL, while holding the duchy is another matter), I'm not sure he could have done the same in England without clear support and legitimacy there as Henri Bauclair had enough time to set up his own bases and interests in England (heck, he did screwed Cliton out of his marriage trough agreements with Rome) whom Etienne would have beneficied in this ATL situation. Considering that Guillaume didn't have the best reputation among Anglo-Norman nobility already, and may have less so if he took Normandy, I think it would at least require some mild equivalent of the Anarchy, where Guillaume Cliton would be disserved by his lack of political power base in England, and political skills alltogether.
Indeed, his death isn't really butterflied away, or rather the causes of his death, as the rebellion in Flanders is due to his own bad management of the county, as he tried to mobilize ressources to conquer Normandy.