I had my Silver stolen once. When I did detective work, I found the guy that stole it and challenged him to a battle, using my Crystal Version. He accepted, battling me with my own Silver Version. We fought on the condition that, if he won, I'd have to give him my Crystal Version too. If I won, I would take back my Silver Version and forget this ever happened.
I had to admit, seeing "PkMn Trainer Sam wants to battle!" looked odd. But, I managed.
It took almost an hour, but I eventually beat him and won my game back.