Actually, the fault would be mine. Just considering the actual POD we were given for this exercise, the deaths of Henry or Jane were the only two scenarios I could think of which would prevent their marriage. Jane's death changes little in the immediate future. Henry's death causes a power vaccum in Europe with a massive prize on the table and an opportunity for Charles to truly destroy his hated rival, or for Francis to gain new weapons to, well, destroy his hated rival.
Charles doesn't trust Francis at all. This is a man who has already blatantly broken one signed agreement and who in 1536 was already supporting Protestants in the HRE and in the process of signing an unprecedented alliance with Charles' OTHER hated rival in Suleiman the Magnificent. With Henry's sudden death, Charles has a small window in which he could finally, finally destroy Francis once and for all if he could manage to get a Habsburg-friendly marriage agreed to with Mary, who is likely going to be crowned Queen of England at 20 years old and with at the time will look like she could produce heirs, spares, and daughters. He will settle on a Scottish/English marriage so long as he likely has a written agreement, signed, sanctified, whatever, that England-Scotland will drop any and all ties to France and at the least remain neutral, or if he can get James to switch Scotland's own allegiance. He needs that guarantee, because without it, Francis still has that backdoor into the Scottish monarchy, that annoying little Auld Alliance, based on centuries of history against a mutual enemy, to try and do whatever he can to re-negotiate that alliance and simply point it against Charles. This is Francis we're talking about, this is a man who has stopped at nothing to try and defeat Charles. Charles probably views this man as a true enemy of Christendom, who has betrayed his faith TWICE, and he's just going to trust that one of France's oldest allies, with old historical ties, won't decide to continue that friendship if Francis throws all the gold in France at him? Charles will take any chance to crush Francis, if he can't get that, then he needs actual written assurance that James won't ever come to Francis' aid.
