Perhaps there is some bug in the WMF's servers which is causing us not to see certain people's activities. That'd explain both how Jimbo's direct involvement in English Wikipedia is steady and how Jayjg is not absent (which Jimbo claimed during one of those last posts in August).
I don't think Jimbo claimed he wasn't absent, he claimed he wasn't AWOL, which is different. Jayjg clearly wasn't on Wikipedia, but he hadn't disappeared without trace.