When ( not if) a blade catches the wheel, it will try and go around. With a guard in place, it will twist out of your hand as it strikes the guard, possibly removing part of your fingers immediately, and then doing one of two things. One is go into the guard and come out the top aiming directly at you at about 100MPH ( small knives will do this in a fraction of a second). The other is for the blade to jam against the wheel, cutting it up, possibly breaking the blade , and sending all this shrapnel at you at 75MPH.
If there is no guard, the blade will most likely be thrown down on the floor behind the buffer. Ed Fowler used to keep a big pile of old belts on the floor behind his buffer to cushion the knife's fall.