This happened to me once a long time ago and the only way I could get my errant officer back was to reload from an earlier patrol. This ticked me off but it didn't happen again, until yesterday. Once again I had to give up my last two patrols to find a save that had all 5 officers. That worked but I was so frustrated just started a new career.
What is really confusing is why I had to go back 2 patrols. It retroactively erased that officer from previous save games that had shown no problems.
Between all the CTDs and now this, I am about ready to give up on this very fun but horribly infested game.
Good luck. If you figure something out let me (us) know.