I've had the same problem with the green chromis. Couple months later there are none left. Never figured out where they went. I don't bother with them anymore. I added 6 yellowtail damsals to my reef tank on June 10, and they are all still there.
This is the first time I've had these damsals, so far so good, and they seem to get along well together, and with the rest of the tankmates too.