I understand your dilemma but on the other hand, you took the pig on aware that these things can happen, that pigs can get sick. There is nothing to say that the next pig you get won't have some medical condition.
I have to be completely honest and say that I would not trust PAH, some branches may be ok but it's not consistent in the chain, other branches are not suitable. Due to these inconsistencies, for me, that puts a black mark on the entire chain of PAH stores. Not fair to tar them all with the same brush, maybe, understood, but it's a chain , to me that includes the notion I would expect the same level of care as standard in every single branch. There is also the issue that you don't know where the pig will end up, whether that be before or after the treatment.
I know it is entirely your choice, and it is up to you to decide how much you trust your local branch. There's no easy answer and I do feel for you.
Regarding the abscess, this can be lanced and drained with no need for surgery, although I accept that in some cases there may be exceptions.