Thankfully I discovered it soon after, since I intended to deposit the checks at an ATM at the airport, and could phone the issuer of the check and have it stopped and reissued. But I was well past the checkpoint by then. I had made sure the checks were in the bag just prior to going through the checkpoint since it occurred to me to use an ATM to deposit them.
Sorry you had to go through that. Anyway, if your bag had been locked and the thief had needed to cut it to get to the checks, he'd probably have been less likely to steal them and more likely to be caught if he had, no?