Haven't spent a lot of time on displacement tests yet as will be working on a website project this week and when it's done will prob get maya 2008, so settings may well be different anyway.

Do you not have any incremental saves that do work or are all your digital eggs in one virtual basket?

did you create any displacement maps for your creature as you may be able to displace the model back in Zbrush from the base mesh assuming you exported the mesh.
Otherwise, yes you're screwed and have to start again, doh.

Gio