The doctor you mentioned is either attempting to cover his tracks or isn't very knowledgeable about guinea pigs. It is absolutely unreasonable that you weren't prescribed antibiotics after this procedure.
There is of course no guarantee that the pig would have survived after the surgery if she had been receiving antibiotics - it's a very traumatic surgery and sometimes their bodies just can't recover - but I do think the doctors that performed the surgery should have done more to ensure, to the best of their ability, that they'd taken all precautions possible to give her the best possible chance of recovery and survival.
Failing to provide follow-up antibiotics after a c-section is just negligent, in my opinion.