I would have to say the Dems are favored to win, whether Biden or someone else if Biden can't make the campaign due to health issues perhaps. From the moment Trump was elected they have had the wind at their backs politically, coming close to winning a variety of GOP held congressional seats in 2017, gubernatorial wins in 2017, easily winning the House and great lake state governorships in 2018, winning Kentucky and Louisiana governorships in 2019. I would put true odds of a Democratic victory at around 4 to 1, not the close to even odds that we have now in the betting markets. Will probably go all in on Trump not to be reelected at around 50 50 odds at predictit. Even if Trump cured cancer and brought world peace there is such a huge amount of people, close to a majority who wont vote for him, just as there is a smaller group, not that much smaller, but definetly smaller, who would vote for him no matter what he does.
I like the fact that noone one so far has said that Trump will try to cancel the elections and declare himself dictator for life, which is what any self respecting 1930's style totalitarian dictator would be trying to do once they took power, let alone were facing imminent defeat.