Don
You and Bill obviously have a good, trusting, hunting relationship to go after buffalo without a backup firearm. I would caution, though, about making blanket statements regarding the wisdom/risks associated with that, and one's ability to outhink the buffalo. I never felt in danger in the three weeks I was with buffalo, and I stalked them quite a bit on my own when pig hunting (but I wouldnt have shot one without a PH)--but then that's only 3 weeks of experience. The outfitter/PH I hunted with has had quite a bit of experience (approx 150 buffalo kills while guiding) and has LOTS of respect for the unpredicatibility of buffalo. He had to kill a cow last year that charged, unprovoked, and "came out of nowhere" from a patch of grass. He and the bowhunter didn't know she was around 'till she came out of the brush at 15-20 yards full out. Four head shots later from a .375 or .416 (dont remember which) she was dead within feet of them. Sure that doesnt happen very often, but I've never been one to trust that bad stuff "only happens to the other guy". Rick and I watched a young bull chase one of the landowner's horses all around a pasture one morning. The buffalo meant business. Why in the world he was chasing a horse we never figured out, guess he was just in the mood. My point is when a hunter screws up (me, you, or anyone else) it is the PH that has to put his ass on the line in the pandamus palms and sort out the gut-shot buffalo. These are big, unpredictable animals. No PH worth his pay wants to put a bullet in your arrow shot buffalo--that said, my opinion is trust the guy with the experience to do the right thing...I couldn't live with myself if a PH or guide got hurt to save my ego and "not put a bullet in MY bowshot buffalo". One of the real risks of hunting dangerous/big game with archery equipment is the possibility of needing "collaboration" from your guide. It sure would beat sending someone to the hospital.
Good luck on your hunt, and stay safe.
Later
Ryan