I've divided and repotted my boyfriends' "old" peace lily this spring. I cut ALL the leaves and most of the roots because they were rotting anyway. It took several months before any signs of growth and now I have two beautiful young divisions and some others that are sadly left outside because of no room (they're slug dessert atm :S ).
Just cut most, if not all leaves, away because the root system cannot support it anyway and give it time. That's all you can do at this point.
