If the computer goes down, the machine stops.
If 120V to the controller goes down, the magnetic switch keeps it off when power returns. When the controller goes down, it also controls 220V to the spindle via a relay. When power goes off, the 220V goes off. When power comes back on, the 220V stays off.
If I lose power, my piece will probably be OK, but only if I can ensure exact zeroing. I have not yet had it happen (other that during testing), so cannot comment, if I have a throw away project or not.