I'm unconvinced. If Biden were to step aside it might be in favour of Andrew Cuomo, if he wanted to run. They are buddies, and Cuomo's stock has been rising recently. Another Clinton run would be disastrous. Unless it's Chelsea.
Both scenarios seem a bit far-fetched to me. Inserting Cuomo or Clinton would further infuriate Sanders' supporters who seem as next in line, and fracture the Democrats worse than before.