Based on historical precedent — both decades ago and more recent — I predict an icepick in Mr Prigozhin's relatively near future.1
Once upon a time, Leon Trotsky "voluntarily" exiled himself to another world capital after opposing Stalin. He made the mistake of establishing a regular location, regular habits — basically, acting as if he could just continue his life as an exile. He got the icepick a little later, after several other attacks on him… primarily motivated by both Joe the Georgian's grudge (one of the biggest "well, duuuuh" concepts in modern European history) and the increasing effectiveness of Trotsky's persuasive efforts at distinguishing "loyalty to Stalin" from "loyalty to the workers" among potential converts to communism/Stalinism.2
Once upon a time, Alexander Litvinenko "defected to the West" and, a few years afterward, drank some tea that didn't agree with him. The connection to Putin is still hazy but somewhat more direct, in that the attack was carried out by successors to his former colleagues from when he was Rezidant in Dresden… in contrast to the frustration he felt as the "silence from Moscow" that prevented a Soviet armed response.
Once upon a time, Sergei Skripal and his daughter fell asleep on a bench in Salisbury, England. Skripal's "crime" was, again, disloyalty to Putin in a rather personal way reflecting directly on Putin's own past.
The collateral damage of this particular — incident? — with Prigozhin is that it points out a serious failing of all dictatorships: The lack of a clear line of succession that does not require (whether factually or culturally) use of force against those who see themselves as the proper successors but are not so selected. And given the NBC stocks (and, as noted in two of the incidents above, willingness to deliver them) in Russia, that's rather distressing.
There's probably already a betting line on both the timing and method of Prigozhin's impending demise. I put the over/under at the shorter of 15 months from today or 15 weeks after Prigozhin publishes, under his own name, any piece exceeding 1,000 words in a Western publication (so long as he stays in a Russian puppet-state), and the method as "more violent than mere poisoning."3 And it will matter not at all whether Putin is still in power, for whatever reason, when it happens: The apparatchiks will continue to take offense at the disloyalty, and will find a way to rationalize that they were "authorized to act."
- This meandering musing relies solely upon open, nonofficial sources. It is certainly not an "intelligence briefing"!
- It's far from certain, but there's some reason to believe that Stalin's regime was beginning to collapse internally around the time Mercador carried out his orders in Mexico City… and that the German invasion in mid-1941 provided the external enemy and threat needed to slow/stop the rot.
- So as to encourage the others, certain assassinations need to simultaneously be both obviously assassinations — at least to those who are to be encouraged — and plausibly deniable. I'm afraid that neither 210Po nor Novichok maintains any of the latter… plus, a more-violent attack would seem more "out of character" and would require involvement of fewer people.