What If...US Election Questions

The US Election is a year away and the question being asked is as Donald Trump is facing 91 criminal charges in four separate trials which are all likely to take place next year, if he ends up in prison, can he still be President?
According to media outlets in America, it depends on whether he is convicted on Federal charges or State charges, Federal charges and he could pardon himself but if he is jailed in one of the two state cases, he would have no power to but being an inmate at the time of the election doesn't exclude him from still running in a presidential election which raises the weird situation of being President and a Prison inmate.
If his lawyers manage to delay the trials until after the election, as they are trying to do, it would be almost impossible to prosecute a sitting President which would mean at least 4 years until the cases could be picked up again which leas to a second, more uncomfortable question as by then Trump will be 82
in 4 years.
It has been mentioned many times that Biden and Trump are old and although Biden is looking increasingly doddery and Trump showing early signs of mental challenges, there are no declared health issues but what if something did happen to them in the run up to the election?
According to the American Constitution, if either of them died or falls seriously ill after 1 January 2024, then they would still be on the ballot because you can run while dead or hospitalised even if you can't be sworn in and there is a precedent for it.
In 2000, a Senator was killed in a plane crash on his way to a campaign event but was still elected and 'served' until a special election was held 2 years later so it seems that neither death nor prison will prevent Biden or Trump becoming the 47th President.