Take him out, put him in a quarantine tank. Do not use a heater, the water needs to be cold, high 60's or so. I had this issue with my Amph, it cleared up in about 2 weeks, actually I think about a week but I gave it another week. One thing I noticed is, once the water temps went back up, he got it again. I'm thinking this fish will always have it. I keep my tanks around 76 degrees now and it went away for the second time. I also used salt and filtration, no other meds. But yes if no action is taken, he will die soon.
That white spot of his face will most likely explode soon and it will start to eat his face a little. Once it goes away, if you are that lucky, he will be left with a hole in his face but it should grow back. My Dempsey had this and my Amp species. Both are still living but I did lose a few other when I didn't know how to possibly cure.
I also did 50% water changes every single day, it's easy when they are in a small tank. Remember to add salt back.