They couldn't "lose" it, they have to give you an FP number these days, there is a clear audit trail from the moment you hand it in to the cop shop. That stuff is a thing of the past
Police do lose evidence, documents etc still.
They dont give you a receipt for evidence, even if they did lose it, they would have to compensate you or the rightful owner, one of the two of you has legal claim to the money, the money would be their responsibility, it is legaly in their trust and they would be respnsible for its safe keeping. In reality the money would be banked I think