According to the US intelligence community, there's no strong evidence that Putin is suffering from a terminal illness. It's curious they should make that pronouncement, but I suspect it has little relevance. The CIA in particular is notorious for its inability to see the obvious at times. For me, there are two lines of evidence that suggest Putin is in a race against time. The first line is the many indications of sickness noted in this article, along with the paper trail of visits from Russia's top oncologist and top thyroid specialist. The second line is the timing of the invasion of Ukraine - it was almost the worst time of year imaginable. Anyone with the capacity to wait would have waited until late October when the ground begins to harden with frost, making it perfect for armored vehicles to move quickly and easily over long distances. At that time of year, with winter coming, Europe would be acutely vulnerable to hydrocarbon blackmail and thus far more likely to acquiesce in the dismemberment of Ukraine in order to keep fat complacent self-indulgent Western voters happy.
But instead of maximizing the benefits of timing, Putin squandered them. Partly because he seems genuinely delusional now, totally cut off from reality by his self-imposed isolation and contact only with the craziest of his advisors; partly perhaps because he feels the sands of time running through his fingers.
Whatever the case, after he dies - and I very much doubt he will be assassinated - I suspect Russia will crumble into civil war, as regional barons fight for dominance. And then perhaps Russia will split into several separate nations, each ruled by a thuggish kleptomaniac and therefore essentially just a miniature Putin with more blood on his hands. All in all, the future for Russia - which could have been a real nation and could have enjoyed the benefits of the 21st century - looks very bleak.