Well I mean, when it leaves play, it loses any extra stuff that was done to it - infection, freeze, blessing and so forth. But it doesn't revert to the "card" that it actually is. That seems inconsistent. It's not like it's still a Devonian Dragon when the game is over.
Although now that I think about it, PU is a badazz card, possibly too much so. There should probably be something of a downside to copying your opponent's critters if you don't have the quanta to play them again should you need to.