And, yes, if you can stop the death, figure out what is causing it, rectify the problem, and move the brain to a nice healthy environment, it will regrow the tissue easily.
BUT - you have to stop the death before the whole colony dies, keeping it clean, giving it good flow and light, and good water conditions will do wonders.
Can you post a picture of how its dieing? That will help along with your latest test results (salinity. temp, alk, calcium, etc)