But then every election is promoted as the most important ever.

I doubt that Biden will run again, and I think that the Dems will allow his condition more visibility/acknowledgement to pave the way for a viable primary run against a sitting President if he does. As you wrote, six more years is a lot at his age.

As for Trump, I don't think he'll return to office. If they can't take him down in the courts, he will be assassinated. Especially if he gets to run against a weak Democrat. One way or another, he won't be back.