I think his VP pick, once revealed, will run the campaign, and Biden will become a mythical legend in the process, although he'll never be seen speaking in the present. Should they win (it would take unprecedented cheating, but this is the DNC), Biden will drop out and someone who never even had to campaign will take his place. HRC, anyone? (It won't be Sanders).
My guess is old Joe will have a major presser sometime around June and he will announce his doctor highly recommends he withdraw from the race based on some undescribed medical issue.
He will then toss what support he may have by then to Cuomo, or Mitt Romney, or some other equally stupid person.