AbsoluteFaye's Mantis Tank Build!
They are much more reclusive during a molt than shrimp, I believe it usually takes around a week before they feel comfortable and come back out. The thread I linked to like way back on the first page from NR has a ton of mantis info, and TIki is what I would call a mantis expert and is always willing to answer people's questions.
Edit: and from everything I've read molting is pretty much the hardest thing they ever do. And it's fairly common for them to re appear with under developed appendages