I think you have your wires crossed - Yeltsin died in office left in terrible health. You could use Gorbachev, but then you’re going back to the Soviet era that was completely different, if also not democratic. It’s also not unique to Russia. Autocrats everywhere make enemies while at the top, and retiring in peace is rare.
I guess it’s possible they could opt to ignore a direct attack and just take one for the team, as could the US if China invaded, but in both cases I think it’s more likely the threat is credible. Heck, by that logic, they could launch a limited nuclear strike on the US using the logic that the US wouldn’t escalate next, and win that way.