I was researching a little and states that
ideally the gun should be disassembled and stored that way. But there doesn't seem to be a law
I think it can come down to what you had already done and the discretion of the police. I know a guy in my clay club who had his Perazzi stolen from his car. Same story, gun was in a slip under clothing etc but they smashed the window and off they went. Police found it a few weeks later stowed away under a mobile home

. The gun had rusted to pieces but he managed to restore it and get the bluing re done on it. I don't know how he did it but he seemed to get off fairly lightly I think. Still has all of his other guns - so there's hope for the OPs friend.