I would put them inside of a large garbage can and water them with some fish fertilizer or miracle grow that has that hormone to stimulate new roots, soak them very well for about 20 min.... and keep on watering them, I bet you they will come back. I have some I planted a year ago, large airlayers. they appeared to be dead also, with watering and warmer days, they are pushing nodes for leaves.
I hope yours do too. they will. Best luck.