That's the thing - you don't attack him at all, just his invasion. He himself may be suicidal, but do you think all his kronies will sacrifice literally everything for him? For what? Some Sunflower fields? There's a reason hardly anyone from the Moscow/St. Petersburg region got drafted - that's where his power base lives. As long as they are not threatened by his invasion, they will play along. But if his games cause them serious damage (which is decidedly not the case currently!), they will not play along anymore.

I'm absolutely willing to call Putins bluff. He's ultimately a coward and not that stupid. He won't do it.