They will continue hiding Biden until the Dem convention. Then soon after some medical or other reason will come up for him to step down, and whoever his vp pick is will become the new democratic candidate. They have to wait until after the convention, because otherwise dems/the people would insist it goes to Bernie, the person with second highest number of delegates.
This way they can get whoever they want into that position.
They know damn well Biden could not handle a debate against Trump.
Biden is a tool they are using.