I have been there and it is devastating to watch. A couple of years ago, I went through the same thing and out of desperation, I caught the remaining fish at night and gave them a freshwater dip. I then put them in my coral only tank and preyed that I they survive through the night. Lucky for me they did and after a week, I had to put them all in the big tank again due to space and pollution concerns. They are still with me to this day. Still dont know what happened but I think it was more luck then anything else.
Maybe try a freshwater dip for the remaining fish?