Isopods have gills which they need to keep hydrated to be able to breathe and survive. So if the substrate is bone dry all over and no water is left in the water dish, that would mean the end of them.

But if there is some moisture somewhere in the tank, they'll do just fine. I tend to keep a corner of the tank moist, and some of the T's like to sit there at times. They also love to dig around in that area.

thanx, i apreciate the info!