Political parties are private organizations, the DNC since they run the show could turn around and just say ‘these two (Not Sanders!) are our Prez & VP candidates’. The rank & file wouldn’t like it, the ‘hand picked’ nominees would get shellacked but that’s likely to happen anyway. What’s got to be saved is ‘down ticket’. Letting Bernie have the prize would that help or hurt ‘down ticket’? I don’t know!
The conventional wisdom is Bernie being on the ballot hurts us on the down ballot because it brings out the brain washed kids. I don’t think anyone really knows. It probably is safe to say if Bernie’s delusional base believes he got screwed again the rats are going to get a beat down.