I suspect the storage facilities are close to being completed emptied of working or easily fixable pieces and all that's left is scrap/spare part pieces.

They may be receiving, or could receive in the future, artillery pieces from allies (ex. NK) that could change their ability to keep up losses.

Regarding China, I don't think China would militarily invade a stable Russia (not civil wared). I think it's more likely they will economically dominate them, with the implicit threat of militarily/covert action if Russia tries and recover their economic sovereignty in those dominated regions.