T directly answer the OP's question -you stop a Rotax to minimum revs and then switch off both mags. The engine will stop, if you have reduced the revs as far as possible with less violence than might occur otherwise. With my conventional mag type switch I can go to one mg and then off.
Switching them back on would cause senseless damage - as it would with a Lycon.
The 912S is a fierce little engine which normally stops as though it has seized, slowing it as much as possible reduces the strain on the mounts and prop.
Switching the mags back on - in any sort of engine is asking to shock load it, blow the exhaust to pieces or just plain stress it. Doing that on a Rotax is even worst, a high rpm, high compression engine should never be treated that way.