
I would wait a week or so see how it goes then if it appears that pup may need surgery I would ring the new owners and be honest with them explaining what the info the vet has given you ...then its really upto them if they still want the pup , wait or go elsewhere.
I had a pup with a tiny hernia and worried myself sick in the end had her seen by the vet then rang the new puppy owners ..I neednt have worried they were great it didnt worrry them one bit as they have had dogs all their lives and know these thing can happen.