My guess is that Putin, in an act of desperation, would but a tactical nuke on his forces if he came any closer to Moscow and then threatened the same if they started to run. Surrender was the only option. The “negotiation” and “pardon” were just for show.
IMO, they are all dead men if they don’t scatter and run.
I just listened to Col Shaffer say that he suspects the Prigozhin is being allowed to live long enough for Russian intel to figure out who else was connected to this treason, and that his life expectancy is not good at all.