Probably they'll have to dig up the line and repair the break. These days, pool plumbing mostly uses PVC pipe and Schedule 40 glued-on fittings (Schedule 40 is a standard for plastic pressure pipe). Finding the break is the tough part. Fixing PVC is pretty easy. If you have a concrete deck you have to cut through, that's tougher.

If it's simply a pipe, any plumber should be able to repair it.