Oh, total sympathies, we live in dread of losing whatever is DS1's favourite obsession at the time. He got terribly upset in the summer when we were in Ireland because he had left (wait for it) the inside of a toilet roll at my aunt's house. No other inside of a toilet roll would do, it had to be that particular one. My dad ended up getting her spare key and taking him to her house to look for it - miraculously he found it too.
Anyway, glad the party didn't go too badly but about the shenanigans on Monday morning.