Just keep in there. It's just kind of unusual that they'd go with antibiotic therapy for rabbits. The "surgery" he'd have to go through is so extremely minor, we put rabbits and guinea pigs through it pretty much regardless of body condition. All they really need to do for an abscess like that that's right on the surface is to gas him down and then lance it.
The issue with guinea pigs and rabbits is that they very tightly and aggressively wall off abscesses. If you compare them to rats (where 99% of the time you can actually use warm compresses to bring them to a head and clean them out at home), they can actually retain abscesses for years before they become problematic. I once saw surgical photos of a rabbit having an abscess the size of a baseball removed! That "barrier" they put up to wall off the infection is very difficult to penetrate, and Baytril doesn't tend to penetrate very effectively, so typically the infection won't be completely killed and that nodule will keep swelling back up until you go in and remove the entire nodule (if that makes sense?)
There are some antibiotics that penetrate better, but they also tend to have a higher incidence of causing GI upset because they're harsher. They're typically used in cases where surgery isn't an option, or where there's significant concern that they didn't get all of an abscess or that infection has penetrated the bone (like in tooth root abscesses -- our vet will remove the tooth, start them on chlor, and even sometimes pack antibiotic beads into the empty cavity).