If things started to go downhill fast for Russia, for Putin...I'm sure there will be someone or two in the power chain that would have the notion to bump him off and subsequently get an Emergency plan in place...it's possibly even been discussed already from a disillusioned group...or just a lone operator with enough resource to plan it and carry it out swiftly.
His successor is in there somewhere and maybe quite a way down the chain and conceivably more looney than Putin.
Several plans were conceived for Hitlers assassination in the middle of WW2 when visionary individuals in Germany started to see where it was all heading...unfortunately none were successful.