There is a very real risk that if relations with Russia deteriorate further, the Security Council will become more blocked. However, it is worth noting that, for Russia, the seat on the Security Council is a standing source of prestige and Moscow does not want the organization to collapse completely.
In the specific case of the Donbass, this is something that I have worked on quite a lot over the last year. Russia is carrying quite a significant cost, frankly, for maintaining its forces in eastern Ukraine. I believe it is possible after the upcoming Ukrainian elections that Moscow might be willing to compromise on some type of peacekeeping settlement so as to extract itself from costly conflict.