Well, in a similar instance I have asked the cabin crew to take care of the guitars as they are plainly grossly over-sized to bring on-board. Got the evil-eye stare from the musicians (5 kids in their early 20s), but almost all other pax around me looked quite happy and the bins quickly were filled up with bags and carry-ons which were stored under the seat before. Would have been a quite long 7 hours flight with all the bags on the floor taking up any chance to move the feet.

The crew was okay with removing the guitars and send them to the hold, actually the purser called the GA quite annoyed and asked why they didn't took them away during boarding.

No, idea if the guitars were damaged, but too be honest. I don't care! Just buy a decent hard case (ideally a rectangular one, not the guitarshaped) and they will be fine.