I'm not sure the west understands how much of a can of worms the fall of Ukraine would mean. It won't be just changing of the guard, but the full ' we found this and that' that soviet propaganda could bring up, not to mention the refugees. Basically, they could 'fabricate' the reasons to go further right in Ukraine. Not to mention that even if they stop at Ukraine, it will be a constant clusterf**k on NATO's eastern flank., with constant poking and incidents.
As for the nuclear posibility, there's this thought that keeps nagging me that they might actually want it to escalate to a russian first strike just to show they're not afraid to use it and to smooth things out for China in Taiwan as well, as exposing the carrier fleet to the risk of getting wiped out by nukes without it turning into all-out nuclear war would be great for countries that love to invade their 'buffer' states, but not so great if you're trying to 'project power' like the US does. Perhaps somewhere with zero civilian casualties. Snake Island in the Black Sea comes to mind, since it has roughly zero civilians, an Ukrainian military base, and it's close enough to NATO troops in eastern Romania that they'd probably see the blast, do the full fallout lockdown etc. WIth an obvious warning of ' next ones are on NATO bases' . Although, I have to admit, nuclear strike on Snake Island in the Black sea in 2022 sounds more like a Far Cry questline ?
Now, I truly don't know what should be done, but I still don't know if sending more troops in the east is a sensible idea. Could mean getting cut off if Hungary flips and cuts off the access from the west and the Russians blockade by sea etc. Depending on how bad it gets, it might be just a good way to lose a few thousand troops, either by becoming POWs, or by getting wiped out in a preemptive strike. Not to mention that it would be Kaliningrad reloaded. Russian troops roughly 100 miles from a NATO bases would be a massive headache.
As for Putin's sanity, let's not forget that he got to power by bombing his own people, and then assassinating the whistleblowers and almost openly bragging about it .There seems to be a certain overlap between insanity while appearing sane and the willingness to commit mass murder . I'm tempted to say that the Soviet Union seemed sane by comparison, but I don't know. And there's no guarante that if there are deeper reasons to this (e.g. oligarchs wanting better deals and Ukrainian resources), someone else might keep the ball rolling if Putin falls, be it Lavrov or some other Lubyanka dude.