Presumably, most experts agree on this on the principle that most leaders are rational, and wish their country to survive. But, supposing a State to be on the verge of collapse, it might not be that surprising if a megalomaniac leader decided to launch on the grounds that "if we go, they go down with us".
I don't *think* Putin's near this point yet. Presumably this War would have to escalate a long way to see such madness seriously contemplated. But it is at least clear that such leaders exist and have existed in the past. Luckily, none of them had access to such weapons.