I have had a spate of bladder stones in my group about a dozen years back when I experimented with diet and for a little while got the balance just out. Thankfully all resulting five bladder stone ops in sows did come off; even the one from the sow with the 'silent' non-symptomatic rabbit-sized bladder stone who was down 510g at the op after another heavy weight loss over the weekend. However, she bounced back to 700g within 2 weeks post op.
Operation success depends majorly on where the stone sits (bladder or urethra in boars), whether the bladder wall of the urethra is majorly damaged and/or crystals are embedded in it (bladder trauma), how long the operation takes plus post-op recovery care at the vets and individual response to the GA. Boars have an awkward kick (inglenook) in their urethra where there stone usually fetches up, which is a lot more difficult and in some cases impossible to operate if the stone has become lodged in the wall.
A straightforward bladder stone op is usually not a problem and a piggy often bounces straight back, just from the sheer relief of pain.
The other issue arises from what is causing the bladder stone: is it dietary or is it something going wrong in the complex calcium absorption process? There is a sweet spot in the diet with a perfect balance of phosphorus, calcium and potassium. Since the food and water intake various individually by piggy as well as by location (water hardness and pellet brand/amount) etc. there is no ideal normal diet that fits everywhere. Going too low in calcium can unhinge the balance just as much as going too high.
If something is wrong with the absorption process, then stones can reform very quickly. The problem is that the only very crude tool we have at our disposal is diet, which takes several weeks to work out of the body and several weeks for new measures to take effect; any changes are not instant. And that some of the things that go wrong with the processing process cannot be influenced by diet and at the best be kept at sludge level from then on in.
This all means that it is very difficult to predict outcomes because of the complexity of the subject and the lack of effective medication. However, without an operation the outcome is a most certain death because there is no way of destroying stones in piggies medically, especially not larger ones, and waiting for them to come out naturally is also a gamble that usually doesn't work. Stones are made of carbohydrate and not calcium, by the way. That is the reason why most stone dissolving miracle cures fail.
Make sure that you ask your vet when you pick up your piggy from the clinic post-op as to how soon he can have more and how much painkiller again, that you have painkiller to give.
Here is some more information:
Wiebke's Guide to Pees and Stones
Tips For Post-operative Care
