With this being a Miltassia, I thought the roots looked fairly good. I would give it a 15 minute soak in tepid water to give live roots plenty of time to plump up. Then check the center clumps of roots (feel if they are squishy). Remove any icky ones. These roots look good enough that I am thinking the way it has been watered may be the culprit. When you water, do you set the plant in a pot taller the the plant's pot and fill with water, letting it soak for about 10 minutes? Then drain and return to it's window?