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.
I wouldn't call the Wii dead, considering the hardware is still selling over 50K a week, nor would I say that there's only one game left to release with selling potential.
For example: Just Dance 4 will sell at least 8 million copies.
The Wii is more alive than certain other recent platforms.
I describe myself as a little dose of toxic masculinity.