Remove any dead leaves and check the roots (and remove any dead roots). You said the leaves are brown...but what about the pseudobulbs? Pbulbs are the green bulb-like structures that the leaves are attached to. If the pbulbs are still alive then the plant has some chance of surviving.
Well you said you overwatered it, so for now, keep on the dry side. Repot in a new mix and don't water too much. If your plant really had lost a lot of roots, then you should try to keep up the humidity. You can do so by putting the plant inside a plastic bag, but open the bag periodically to improve air movement.
Also if the leaves keep rotting, you might have to spray with a fungicide. Good luck with your plant.