Should I repot these orchids with root rot?

[hmomof2]

Hello, I need help! I have two phal orchids that were together in one pot. They were doing fine for several months, until I noticed that there were fungus gnats that would not go away, I did not know which of my plants they were coming from so I treated them all. I then repotted my orchids, and trouble began...
I now have one orchid with I believe severe root rot as nearly all the roots are yellowing. There is only one of the two leaves that may hang around. The other is bad as well however, has a few leaves that look good for now. One recently yellowed and fell off.
I need all the help I can get!