A duplicate of Will Riker that was created in a transporter incident is discovered in the TNG Episode "Second Chances." The next time we see Riker's duplicate is in the DS9 episode "Defiant." We also learn that he is going by his middle name of "Thomas" instead of his first name of "Will" so as to differentiate himself from Will Riker. At the end of the episode Thomas gives himself up to Sisko, and agrees to do hard time for the rest of his life at a Cardassian labor camp.
SISKO [on viewscreen]: The deal is you'll be tried and convicted in a Cardassian court and then sentenced to spend the rest of your life in the Lazon Two labour camp.
RIKER: No death sentence, huh? That must have taken some doing.
After Riker turns the ship over, Major Kira tells him she is going to make sure he gets out.
RIKER: Transmit the Orias Three sensor logs to the Kraxon, and tell them to prepare to beam me aboard. I'm turning command over to Major Kira. She'll get you back to the Federation. I'm holding you personally responsible to see that these people get a fair trial.
KIRA: I give you my word. We'll get you out of there, Tom. I promise you that. (Riker kisses Kira.)
What happens to Lt. Thomas Riker after this episode? Does he ever make it to the labor camp? Does he ever get released or rescued? Do we ever hear from him again? If there isn't anything STU then anything EU, writer's notes, or anything else would be appreciated.