I believe crazy uncle Joe is nearing the breaking point. He demonstrably has difficulty completing a sentence or a coherent thought. I can't imagine him on a live debate stage opposite President Trump. I think the strain of the final campaign push will break him. The closer that happens to the actual election the better. It would give the 'rats less time to regroup and rally behind someone else.
I think we're going to see something weird this election cycle. We're going to see Joe's handlers run a "campaign by proxy" - using others to campaign for him. Sure, previous candidates have had support from others hitting the campaign trail, news shows, etc. for them. But in Joe's case, the more he is kept out of the public eye the better. The MSM will of course be a very willing participant in this - continuing their exclusively negative slant on all things Trump. The MSM propaganda machine will studiously ignore the lack of candidate Biden on the campaign trail and instead provide copious amounts of coverage of any and all people campaigning by proxy for him.
If Joe does surface anywhere it will be in very carefully controlled conditions and only in a very left-friendly environment.