Is it possible for pyloric stenosis to 'come back'?

No: It is possible to have vomiting symptoms if the baby is overfed. It is also possible that if the pyloromyotomy is not done correctly. Ie complete muscle sectioning that residual symptoms could persist. Always use a pediatric surgeon.

Usually not: Hypertrophic pyloric stenosis (hps) in a young baby is treated with an operation called a pyloromyotomy. The hypertrophic circular pyloric muscle fibers are split to open the pylorus & allow the stomach to empty. If done well & thoroughly, hps should not return. One occasionally hears of a case of recurrent hps, but often, when looked at closely, it was an inadequate pyloromyotomy to begin with.

Very rare: Recurrent pyloric stenosis is extremely rare, 0.07% in one study. Some believe related to incomplete surgery of pyloric muscle I have seen it occur extremely rarely with very experienced pediatric surgeon.