Hi dcholakian, welcome to Cruise-Chat! Sorry to hear about your problem. Princess is not going to return your cruise fare, you did indeed receive what your contract was for, a b2b cruise. I am very glad they caught the thief. I am truly surprised anyone on board would jeopardize their job for a laptop that can be purchased so inexpensively. You can rest assured that the person who did violate you is no longer working for the cruise line.
Gary has some sound advice. Do not send a letter that is threatening, do not stipulate that they should compensate you. They may pay for your data recovery, if you word the letter properly.
I do hope the rest of the cruise was satisfactory and that you do not hold the entire cruise line at fault for the actions of one stupid individual. Best wishes!