what to do if a mindslave mindslaves the person who mindslaved them

[Spy_Guy]

If it happened by mistake (implant gun misfire), then due to the deep-seated loyalty of the original mindslave they would recognize their error and correct the issue asap.

You can't simultaneously implant eachother, since the implant itself applies a stun, so that's not possible either. The first person on the draw wins it all.