ditto to mattyice. when a mantis molts it can hole up and not eat for a while. day, week, two weeks maybe? it really depends on the individual mantis' species and size mostly.
so don't give up hope yet!
just make sure you DON'T bother it!!! don't shove food in the hole, don't siphon, dont do a water change, and dont even try to peek in for a look-see. seriously. You can easily kill a moulting mantis by freaking it out. during a molt, the otherwise near indestrctible mantis is in its most vulnerable state. be gentle, be patient.