Why would Count Baldwin V of Flanders marry his daughter to a displaced baron who failed to displace a bastard duke from the throne of Normandy? That seems a bit of a poor catch from a diplomatic standpoint. Also, if William dies, Normandy does not go to Gui de Brionne unless by force, which Gui cannot provide.
William the Bastard was only able to invade England due to a shaky claim that, when Harold Godwinson was shipwrecked in Normandy in 1064, he gave his claim to the throne upon Edward the Confessor's death to William. This was impossible in English law, by which the next king would be elected by the Witengamot - Harold didn't inherit the throne in the Norman sense. Moreover, Harold denied this promise ever happened and there was no physical proof. What I'm saying is William's claim was very weak, probably fabricated, and not something any Norman duke would have or act on.
I suppose that any duke of Normandy in 1066 could invade England, but it's not particularly likely. And if Gui has somehow become duke, I suspect he'd have enough on his plate on his side of the channel.