jezus christ, no one ever mentioned anything about a "world ending" scenarioWell it would almost certainly be a limited action, tactical. Not world ending.
But he could start WW3.
Shit would really hit the fan and many countries would gather together to end him. If he uses nukes he's signed his own death warrant.
Who he would try to target first(and to your point the last)
Look what happened to Saddam Hussein, Putin actually has the weapons Saddam was accused of having and everyone is mentioning Putins off the deep end