Even though the culms don't look entirely dead to you, I'm not sure they will recover. F. nitida is one of the hardiest bamboos, but it's only hardy to minus 20F and your Zone probably exceeds that during the winter. All you can do is water it normally and see if it puts up new growth. Pruning it back will not make any difference, so you might as well leave the exzisting culms alone on the off chance that you may get a little foliage back. The big question is whether the rhizomes died during the winter. Give it this growing season to see if it has any life in it. If it makes a comeback, it would be good to bury it heavily in a pile of mulch in the fall to try to protect it during winter. Unfortunately, your Zone may be too cold to keep a bamboo alive outdoors through multiple growing seasons. I don't recommend starting over at this point because another F. nitida will not do any better. Good luck.