Since the system is isolated, and that no heat comes in the system or leaves the system.
We know that water freezes at 0 and ice also melts at 0. The difference between these two is the latent heat of fusion. Water at 0 has more energy than ice at 0.
What would happen is the second law of thermodynamics (entropy) would take over. Some of the ice would melt, and some of the water would freeze. But the TOTAL MASS of ice would remain constant and the TOTAL MASS of water would remain constant. They would continue to change shape and tend toward disorder.