Is her voice gone or does she just choose to be lazy?
Sure, last night's performance was an embarrassing mess but mostly because of the fact she chose to lip sync and they didn't play the backing track, so instead of choosing to actually sing it she just walked around stage looking lost.
But then last year she just gave this performance and her vocals were great:
Honestly her vocals have not been as good as they "used to be" since TEOM era imo, but she can still sing, right?
Of course she can still sing. But she's not going to when she can't hear herself on stage. just go on youtube and look up mariah carey live 2016, tons of live performances where she sounded amazing.