If the vet is experienced, guinea pigs do as well with surgery as any other species of animal. However, with a bladder stone the longer you wait, the more dangerous it is. If the stone moves into his urethra, it WILL kill him.
We are as gods to the beasts of the fields. We order the time o' their birth and the time o' their death. Between times, we ha' a duty. - Terry Pratchett.
"Men have forgotten this truth", said the fox, "But you must not forget it. You become responsible, forever, for what you have tamed. - Antoine de Saint-Exupéry