I think it would undermine their further security, defense, and foreign policy regime. Already we are seeing these structures eroded at a pace that is faster and faster, and we are not creating any new structures. It wouldn't encourage proliferation, but it would encourage China to build up even faster. It would encourage Russia to keep more weapons. It would encourage others to get around the missile shield.
Proliferation is a different matter.
One of the regions where I think American leadership has failed miserably is on nuclear proliferation, neither to persuade India and Pakistan. When they started to proliferate, we all decided to disregard them. That was a failure of American leadership. The most important thing Russia faces is not necessarily economic disasters or theft of nuclear weapons, but pulling out of the technological revolution and the new industrial human education revolution. Help integrate Russia into the world.