Barron tested negative, if that matters.
What happens if Trump dies is that the RNC puts up a new nominee. Anyone who has already voted for Trump still counts as a vote for Trump and not the new Republican nominee, and this late in the game, any hope that nominee has of getting the vote depends on a write-in campaign and/or faithless electors, because most of the ballots have already been printed and aren’t likely to be replaced.
If there’s no clear winner, or there’s an ungodly mess where the results can’t reasonably be considered legitimate, or Trump somehow wins despite having a bad case of the deads, then it’s up to the House of Representatives to pick who’s president. They don’t have to choose anyone actually running, and Pence only gets to be President until Jan 20th unless the House picks him for some strange reason. I strongly suspect Biden still wins in that case.
That’s assuming that the Supreme Court doesn’t meddle in the election like it did in 2000, which it probably will if Barrett gets rammed through before Trump dies. Then, who the hell knows, but it probably wouldn’t be good.