So, marine gave his notice. When S tells me this, a small smile twitched the corner of my mouth, then was suppressed. S saw, though, and tells me this has been the usual reaction. We talked later, both relieved that he had not been fired and escorted out by security. Both admitted to each other our suspicions that he really is the type to return, armed and begrudged.
I really was afraid of what he was capable of, and I'm very relieved that he will be gone.