It's not so much a matter of Nicholas merely living longer as it is outliving Charles the Bold for its unlikely that Mary would be married to anyone while her father lived so crucial was she as a pawn in his diplomatic intrigues. She was promised to no less than half a dozen people, each cast off when someone else came along with more to offer Burgundy. Mary's engagement to Nicholas was mainly made to prevent Nicholas from marrying Anne of France, daughter of Louis XI, and thus put Lorraine into the Burgundian sphere. IIRC it was abandoned before Nicholas even died and in any event as soon as Charles set himself to being made King of the Romans Maximilian became the premier candidate.
But even supposing the marriage does happen Nicholas isn't likely to loose Provence, as his father still rules there, at least until 1480. Anjou is likely to be occupied if he quarrels with Louis but Louis has less claim there with a living male heir to Rene. But the Duchy of Burgundy and the Somme towns will surely go and Louis will also press for Artois and Flanders which are theoretically French fiefs. How much of Mary's inheritance is lost likely depends on how well Nicholas fares against the French on the battlefield.
I don't see how or why Nicholas would claim the French throne, as a cadet Valois his claim is based on salic law yet under salic law there are many people ahead of him. Outright conquest of France by force of arms without legal pretext seems equally unlikely. Besides he already has pretensions to Sicily, Naples, Aragon and Jerusalem while being ruler or heir to Provence, Anjou, Burgundy, Lorraine, Bar and the Netherlands, isn't that enough?