If the tortoise has a bladder stone, eventually he won't be able to urinate. He will stop eating and die. Sometimes the vet can reach in and break up the stone with forceps, but more often than not it requires surgery.
There are a variety of ways to treat it, but all involve a vet. Best to find a good tortoise vet. They can sometimes break up the stones without surgery, and other times they have to open them up and remove the stones.