Possible? Yes. If it did, I would think they'd get out. I've not yet heard of a case of a tortoise cooking itself in hot water. Sulcatas do not have a mechanism to tell them its too cold and they need to find warmth. They do, however, have a mechanism that tells them its too hot, and they need to find somewhere cooler. This is why they are perfectly happy to park under a bush on a too cold night and stay there and freeze, but let them park under that same bush on a really hot summer day, and they will run for cover once it gets too hot.