Actually, what do we actually knows?
The Russian news agency publicly stated that Prigozhin was on the manifest on a plane that crashed. It's like TASS want the world to know he is dead (or think that he is dead)
Problem is, I would kill Prigozhin too if I am Putin, in fact, many of his inner circle pressure and remark that Putin is too soft on Prigozhin, that Putin should have killed him months ago. Everyone of us saw Prigozhin is a dead man walking a mile away. Problem is, if Prigozhin is disappear and his body wash up somewhere hush-hush, or had the FSB leak Prigozhin iterary and have the millions of Ukrainian that lining up to kill him to do the deed? that I understand, but killing him like this and want everyone knows? That is going to make him a martyr.
I mean, unless Putin is now going to the frontline and direct the troop on the ground himself, he is going to need to put the troop on someone that will do it for him. Again, if you are taking over Prigozhin old job, and then this happen, would you think "oh I better do what Putin said or I will die" or "why not I use the power I had to kill the old man himself first before I too was shot down or thrown out of window" There are tens if not hundred of commander with troop on the field, you don't need all of them to think of the latter to have another coup, and if that coup happen, this is going to be all the way. Unless Putin is REALLY that sure there will not be any opposition, killing Prigozhin like this is extremely stupid.
On the other hand, do we even know if he is actually on the plane? Because the "name on the manifest" is the oldest trick on the book to fake death, for all I know Prigozhin could be in one of those CIA black site debriefing the American.