Anyone who is able to consolidate enough influence to actually kill Putin could be much worse. Unfortunately, that isn’t the worst that could happen.
The people are going to need to pull off a classic revolution and eliminate Putin, his generals, his army of oligarchs and any other warlords that may be in waiting.
If Putin was to jump out of a window by himself there is going to be a turf war in Russia so big, it’ll make the bolshevik revolution seem like a wholesome bedtime story. Other countries will need to jump in just to make sure that their nukes don’t get sold to any jackass with a few hundred grand.
Even worse, if Russia ever gets that weak, China may try and step in and take over. Or, any other country that feels froggy may try and assert control somehow. That’ll be messy.