I don't think the show must go on applies in this situation where she was clearly incapable of performing and shouldn't have been allowed to.
The only people that profitted(sp?) from this debacle are Zalon and everyone that works for her, and they made money at the expense of her reputation and dignity and the public's hard earned money who payed to see a worthless show, didn't get their money's worth and as far as I know haven't been refunded and won't be given the money that's now in Zalon and co.'s pocket. It's despicable from beginning to end and I don't see how anyone can justify the people around her at this point.
Another poster made an excellent point, if the band, manager and her crew were to say, "No, Amy, you're not in any shape to perform. We won't do it!" What do you think would happen? The record company would say, "Fine you don't get paid, period." Then, probably a new batch would be hired, and the same thing would happen. The band, manager, roadies, etc. work for her and the record company.