I think I would have to have questions answered before making that decision. Were there stones, or just crystals? Do they think they got them all out? What is the percentage chance that he would get blocked up again? How well did he recover from the procedures they did, and how is he handling the environment - is he groggy or upset? Ultimately medicine (animal or human) is an art as much as it is a science, and there are very few guarantees either way, but they ought to be able to give you an informed opinion. That is what you are paying them for. And if the vet isn't there, I bet she is available by phone, at least to them.