I don't think there would be much protest if Adam went over Angela R. I'm really rooting for Adam but that rumba wasn't great from him, and for the casual viewer it'll look even worse. He doesn't have a fan base who'd riot.
Based on the judges scores Adam scored
6,7,7,7 and Angela R scored 7,8,6,7, so barring a terrible cockup from
Angela in the DO (highly unlikely in a waltz) it's entirely plausible that three judges would save her with a consolation vote for Adam from Shirley.
I agree that if his RA problems are getting worse he should probably go before he had to quit. I remember Ugo Monye who had terrible back (?) problems was given an almost immobile Rumba before being swiftly voted off.