@engineer,
I find it hard to be confident just where Sander's support would go were he to disappear. That the 25% or so of polled Democrats who appear to have continued their support for him, in the face of the emergence of 20 plus new candidates, most of whom are advocating very similar agendas, remains a stunning fact. I readily agree that the Democrat Party leadership would choose Biden over Sanders in a choice between the two, and that Biden would likely be a stronger candidate than Sanders in the contest for the Presidency.
The remaining alternative remains the emergence of one or two of the crowd of progressives below Sanders. However, so far there are no indications of that happening . Instead each new candidate appears to get his/her week or two in the political spotlight and then fades into the background (remember Beto?). The months ahead, and the initial state primaries, certainly offer opportunities for a change in this situation, but it is more than odd that nothing like it has occurred yet.
This is a serious dilemma for the Democrats, and I suspect the scenario you described leading to Biden candidacy may well be the result.
That said, in a Trump vs Biden contest I would bet on a Trump victory.