I've heard and seen in other threads that WotC is not very helpful whatsoever in replacing lost parts. Doesn't matter how much money you want to throw at them. Not even very helpful in replacing damaged components upon opening a sealed copy. But you never know. Good Luck. Hopefully your friend will find your original piece.
I'm sure some have had bad results, but I have to say my experience was quite the opposite. My copy of Ravenloft had 2 extra minis, but meant that I was 2 short on others (one being one of the heroes!).
I sent an email through their website customer service, and within 2 weeks had brand new figures on my doorstep. No muss, no fuss.