I've been stuck on quite a few rides before, but most of the time I'm really unlucky and am right at the front of the que when it brakes down! I've only been evaced from one ride which was Loggers at fright night last year. It wasn't on a lift hill though, it was at the bottom of the lift hill, but we got to walk down the old CCR track and got free fast tracks!
With Vortex, once for me it did like 2 small swings at the start, then stopped and the floor came back up about halfway, but then started going down again. Then it just started again and was fine! I think the operator might of emergency stopped it by accident maybe? This was in the 2012 season.