on a tie: they take out the guards, but make too much noise and they know it's only a matter of time until one of the bodies are found -- the group is free of guards, but that's only going to last for a minute at most before the place goes on high alert.
on a fail - they get discovered and the alarms are set off. they may still take out most of the perimeter guards.
on a HUGE fail (like, by -3 or more) - they not only don't take out the guards, they get caught by them and held hostage.