I've just been thinking about this.
A plausible scenario is that China agrees to pay off the debts as they come in return for as yet unspecified favours. They have form of doing similar in Africa.
This week has confirmed to me that Russia is in it's death throes as a serious international player. I think they'll end this war as little more than a vassal state to China, who would love a country with a seat at the security council, a deadly arsenal and an endless capacity for doing dirty work under their thumb.
The West v China is shaping up to be the real battle of the century ... and Russia are a pawn in this match
This is kind of where I am - I cannot see how Russia gets out of this. This isn't over quickly - and the longer it goes on the more screwed they are in terms of military resource and death count - and economically they are cut off with practically no import / export, can't participate in global markets etc