What happens if a candidate becomes incapacitated during a campaign?

Seems to me the party would nominate someone else. The thing about the VP taking over for the President doesn't apply here.

The Party should have some rules to figure out who would run in their place. It would probably be close to the old school smoke filled room discussions of who would run.

Their approval rating goes up.

The Party gets to decide what to do. The government's job is to carry out the election. The Parties participate within those rules mostly on their own terms -- they don't even have to participate if they don't want to, but they usually choose to do so.

The committee has to choose another candidate.

Joe Biden will pinch hit in the 9th for Hill.

no idea