People say that if you cover the dying tissue with super glue gel it may slow or stop the RTN.
Keep it in the tank, by all means, it can't hurt. I've had a small colony of acro that came in already "RTNing" and I am seeing that the tissue that remained is polyping out.
If the coral grows back out, it will be more hardy.
There are some acros that have a lot of white on them, along with some sort of color though... I'm not entirely sure what to say, a picture would really help.