But… Russia isn't the only place causing oligarchs to have quote marks around the word "accident", it's simply a state that's bad at the coverup.
I don't know at what point his private jet suffers a mysterious decompression, or his drugs are tainted with a lethal agent, or whatever, and it's possible his conversations with Russia have included such threats already. But eventually, playing with all this fire, worldwide, burns are inevitable.
There's a reason former US presidents get secret service protection for life, and they're term-limited.
This would all still be the case even if he was just making the kind of waves most of the west likes, rather than… not even just this, also encouraging a civil war in a nuclear armed state.