No, you haven't lost it. You are still PMP certified. The PMP diploma is just for you to show off, but when someone wants to check if you're a PMP or not, then s/he'll check the PMP registry.
You can email PMI about a replacement diploma - I'm sure they'll send one to you. I'm not sure though whether this'll be free of charge or not.
Again, losing the PMP diploma does NOT mean that you have lost your PMP certification, you are still a PMP.