that dry dead spanish moss is going to rot and leave you a big mess..spanish moss is fine as long is its alive and not dead dried moss from the hobby lobby. Dried spanish moss is decorative and adds ZERO to the plant.
The roots did not rot bec they couldnt take the water. Vanda roots can take tons of water.The roots got rotten bec the plant cant use the water you gave it bec of three factors light, heat, and humidity were too low. Vandas are waterhogs outdoors in the sun heat humidity. Mine have been down to too cold temps over the past few years and they do much better outside than inside for sure.
Reminder if a vanda looks like it needs water, You chould have waterd it yesterday