Interesting speculation (hard to confirm) regarding Putin having cancer. But I think your explanation regarding why he attacked Ukraine or the consequences of his actions are less plausible.
I think the timing of his invasion into Ukraine had more to do with Biden being President, the dependence of Europe on Russian oil and gas, and his desire to reassemble the Soviet Union. All of these factors especially in the face of the poorly executed exit by the US from Afghanistan has led Putin to believe the timing was right. America has always been the counterweight to Russia and China since WW2 and if we appear to be passive, it will attract aggression.
In many ways, as Trump was excoriated for pointing out, the "timing was right". What Putin failed to fully appreciate was the resolve of the Ukrainian people and the toughness of their armed forces and leadership of Zelensky. He also overestimated the skill of his military which has not fought a major war in decades (America also underestimated Ukraine and over estimated Russia). The Ukrainian army has been involved in a "hot conflict" since Russia took Crimea with respect to separatists in eastern Ukraine. Not the same as major war, but still a means to "bloody" troops and history shows no amount of training equates to some experience under fire.
As a result, the "quick" war is slowly turning into a proxy war, where the economic might of NATO will potentially grind down Russia, but sadly at the expense Ukrainian citizens. Putin may become desparate, not for fear of losing the war, but losing the support of the Russian people, contending with their husbands, fathers, and sons returning to Russia in body bags or not at all. Without a "prize" for their suffering, the Russian people may cry out for "regime change". Eventually, someone close to Putin will hear their cries.
As for Putin fearing being tried as a war criminal, I don't think that will happen unless his generals and oligarchs turn against him and turn him over for trial as a "peace offering". Right now that seems unlikely, but in time that could change.
I think Putin hoped the atrocities he has allowed in Ukraine would break their resolve but instead it has galvinized support for the Ukrainians and for my part, I hople we give Ukraine everything it needs including heavy weapons and planes. I even support providing "air support", but my "line in the sand" is "ground troops". If any ground troops go into Ukraine they should be European forces.
NATO especiallly the Europeans need to face down Putin with military strength and once and for all make clear to Putin and Russia that Europe will not tolerate seizing land at the expense of other nations. A massive defeat of Russia supplemented by America and Canada fully developing our fossil fuel resources and able to export to Europe in lieu of Russian oil and gas, would leave Russia as a second rate nation better off allying with western Europe than trying to conquer it.
