Retail is by no means dead. BfA is a definite stinker but the people who love retail will continue to love it.
Yeah they are going to lose some amount of players. Some for a month, some for the rest of the expansion and some forever.
Hopefully between Classic, and likely TBC & Wrath, and Modern or Retail that World of Warcraft is strengthened as a whole.
Hopefully after launch the hostility between the two groups will end. I know that I have made a few jokes about one of the camps.