My favorite large technical fail was on the Independence of the Seas.
Top of "Invitation to Dance" - based off of one of those "So you think you can dance" type shows in England which included guest participation based on a dance competition earlier in the cruise. Anyway, one of the presenters from the show had done a bunch of videos for this event, and it was decided to change the format slightly, so we had her on board to re-record them. So the show day comes, she gets up on stage and mentions how proud she was of this show, and about the collaborative works between her and RCCL, the Cruise Director warms the crowd up and the lights dim for show. The automation system completely cacks itself. The main is stuck at half mast, the orchestra is playing away the dancers don't know what to do. 10 seconds later, call to stop the show comes through, CD comes out on stage in a followspot, and he says:
"Sorry folks, the hampster has fallen off of his wheel, our technicians are now behind the curtain trying to get him back up and running. So I am going to stand here for 10 minutes, let him catch his breath and we will get on with the show".
8 minutes later we had declared the automtion system cactus, and the Cruise Director handed me a PPT slide, showing some images of a hampster, he got on stage and said:
"Ladies and gentlemen, it is with a heavy heart that I announce Hammy the Hampster passed away. Unfortunately our cast and crew are too distraught to continue with tonights show, however we will be docking tomorrow, and will find a new hampster and try again tomorrow."
The audience left chuckling, and everyone was happy. I guess with any disaster, it it how you handle it.