At Mesa, I've known of a person getting to redo the entire sim portion, but this is extremely rare.
Think we do two sim zero's now?
Talk of the worst training departments... How about the best? The Mesa instructors are the ones that keep this place going with blood, sweat, and tears. For a new hire, you couldn't ask for a more welcoming, nurturing environment, especially for those with only part 91 experience. The guys from other 121's and 135's will find the experience very chill.
With that said, if you have no business flying an airliner, you will not pass Mesa's training. However, many of our failures have found their way to other regionals and are successful. Perhaps they needed that initial experience to kick their attitude and focus in the right direction.