"Russian elites are allegedly planning to remove President Vladimir Putin (https://www.newsweek.com/topic/vladimir-putin), according to Ukrainian intelligence, with a successor already in mind."

"'In the environment of the Russian business and political elite, a group of influential persons opposing [Vladimir Putin] is formed,' the post reads. 'Their goal is to remove Putin from power as soon as possible and restore economic ties with the West, destroyed due to the war in Ukraine.'"
https://www.newsweek.com/russias-elite-want-putin-out-successor-mind-ukraine-intel-chief-1689830

Other news sources suggest Putin has colon cancer, thus his tired-looking, somewhat puffy face, his care about being not too close to people (green screens when supposedly speaking publicly and long table when negotiating/talking with someone) -- because of concerns about his immune system?

Is this war in Ukraine (and elsewhere?) and winning it his last gasp toward immortality in Russian history?

Last Question first . I have noted that Vladdy has stomach cancer and Parkinson's and that he does see this as a legacy war .
As for the ability of removing him ;I doubt it unless Ukraine forces a Russian withdrawal .

Despite the difficulties Russia is already close to achieving the unstated goals Putty had when he began the war. Those are independent Russian friendly states in the Donbas region including a land bridge to Crimea ;Ukraine not being admitted into NATO , and either regime change or neutering the Zelenski regime . He would've also liked to extend the Russian friendly state as far west as the Dnieper river . That is not likely . He escalated in the hope of an easy victory . But the Russian doctrine has always been to escalate to deescalate . Once he completes the siege of Mariupol then he will go to the negotiation table . He has already extracted concessions from Zelenski to not join NATO and agreement that the Donbas region and Crimea will be carved out from Ukraine .