We don’t know what happened to Ken or Koromaru, but Officer Kurosawa’s story is fleshed out in Persona 4: Arena. If you played Persona 3 or any one of its ports you may recognize Officer Kurosawa since he sold weapons to the S.E.E.S. group from the police station. Mitsuru is working with him in Persona 4: Arena and they’re both in Inaba. Mitsuru seems to quite a bit about Labrys too and artwork shows Mitsuru with two of them?
Persona 4: Arena and its extended story mode comes out on August 4 in North America.