You're assuming Putin is rational. That's not a good assumption. Putin is elderly, likely in very bad health or possibly dying of cancer, and wants to make his mark on the world. In addition, if he loses in Ukraine, he'll likely be assassinated, so he has absolutely nothing to lose here. There's not really a good reason he wouldn't launch armageddon. We can only hope that his underlings don't want to get themselves and all other Russians exterminated in nuclear fire and will refuse to carry out his orders.