I didn't realize it, but I have been vastly underwatering my peace lily. It's always recovered after watering. This time, one day it was fine and then it drooped. When I watered it, some of the leaves came back, but most still droop. I gave it a good soaking (after I read that's what it needed when it was dry). Some of the leaves are slowly lifting, and they look pretty healthy. I cut off the dead ones and the dead parts of the leaves. It's been about 5 days. Will it recover? Does it just take a while? I really love this plant.
Lecia, as you said some of the leaves are still lifting, so give it some more time. But, I suspect some will never perk up to the level they were before. This plant does not like to go completely dry. The good thing is you do have some that are going to grow as you want them. In a week, you can remove some of the leaves that did not stand back up, but never remove more than 1/3 of the plant's green leaves. They may be drooping, but they are still healthy enough to make energy for your plant to live. The stress of the dehydration, may stimulate it to start to make a bunch of new leave or removing a 1/3 or less of the leaves that never stand back up might stimulate it to make a batch of new leaves.
No matter what happens, you saved you plant in time. Eventually it will have plenty of new leaves that are standing up that you can remove all the deformed ones, but never more than 1/3 of the total amount of green leaves. In the future you should keep you peace lily moist at all times, but never wet. You have managed to grow a large otherwise healthy plant. You should be proud of that. Only because it was healthy to start will it recover from this stress.