Who will be the candidates anyway? I don't trust both party but one will win eventually. Good presidents do their second terms, like Obama, and bad presidents can't do, like Trump. I don't think Biden fit in both categories. He wasn't bad but he's too old to re-elect, I don't even think he will be a candidate again. I have to see DP's candidates first.
It seems that in the next election, Biden will again face Trump and this will again be a fairly hot election, considering that these two pairs are people full of controversy. It will be quite difficult to choose who will win, whether Biden or Trump, but considering Biden's declining health, this will be a good chance for Trump to regain his position and remove Biden from his position as president.
If a rematch between those two actually happen, then I am afraid it won't be an election to choose the best person for the charge of the presidency of the United States, but rather to choose the lesser evil.
I personally think that Biden's health won't have any influence on the results of the election, mostly because it seems that there is no serious democrat who is willing to challenge Biden in the primaries and even if there was, none of them would dare to talk about Biden's health, for democrats that is rather a taboo.