Mantis Shrimp is back!

[Tyfighter]

About 3 months ago I discovered a mantis shrimp living in a piece of live rock. After pulling out the rock and trying a freshwater dip, and soda waterfall he didn't come out. I put the rock back in and didn't see or hear from him for weeks so I assumed he was dead (not my intention) .
Last week I noticed a piec of snail flesh floating around, I didn't give it much thought since my hermit crabs are dicks, but today I see two black googley eyes peering out at me from a hole in his rock.

At this point I have some sps that have encrusted on to the rock so pulling it out and a dipping isn't really an option anymore.
I am tempted to just leave it in the rock, I don't mind if it kills an occasional snail, I am just not sure if it will grow or not and start to kill everything. It is about 3" long and all dark grey/black are there any stomatopod experts out there?