Theoretically, we could be looking at a Supreme Court case regarding the 20th and 25th Amendments with a vacant seat which could pressure Congress to hastily rush towards confirming a candidate they may or may not deem qualified for the position. This is absolutely insane.

If he recovers, everything in this thread will be a moot point, but there is a gap in Constitutional succession of powers should a candidate die between the election and when the Electoral College votes. If before the election, Americans could still vote for him (even if dead)

The GOP could vote to have Pence be the Presidential nominee and nominate a new VP (if they win) for Congressional approval after he’s sworn in. Or they could do a 2nd convention, pick an entirely new presidential candidate entirely, and votes for Trump would transfer to them.

I’m not sure what the worst case scenario is, but this is the most unprecedented of unprecedented events in US history. This is going to get even messier.