I don’t see it that way. Bernie has his own little party within a party that doesn’t seem to share a base with anyone else.
In other words, if Warren drops out tomorrow, I’d expect her support to be spread among all the other Democratic candidates (Harris, Buttigieg, Biden, Bernie, Klobuchar...) instead of going mostly to Bernie.
If Sanders drops out tomorrow, I’d kind of expect his support to be spread among staying home, voting third party (e.g., Green), supporting Trump, or supporting fringe candidates like Gravel or Gabbard. I wouldn’t expect his supporters to go to Warren en masse.