if power went out and a machine was running it would not start when the power came back on. The switches take care of that when the coil disengages when the power went off. Anyone running a roto then its even more so as there are other things supplying the power that are not going to start.
I wont be putting a mag starter on my belt sander though, more weight if I enter the sander into belt sander races.
Can a mag starter fail and stay engaged. Yeah it can but its rare. Ive had one in over 30 machines do that when my compressor would not shut off cause the coil had arced in the engaged position. It was 37 years old and its mounted on the compressor so its had its ass rattled off for many years.