Wii is dead. One game release is not going to change that. The only hope Square has of extending the life of the game for that period of time is to make sure the Wii U version sells well and keeps people interested. I don't know how subscription MMO's fare in Japan, but over here in the West they are floundering. Even WoW is dying off. Everything is going free-to-play just to stay alive.
yeah wow is dying off slowly. mists of pandaria, and eventually going free 2 play will keep it above 1 million I believe until 2017-18.