TV producers and Game producers are separate. They make that very clear. They collaborate on cross platform content, but they neither control eachother nor rely on eachother. If either goes down, I'm more than confident the other will live on in it's own capacity.
Yes they will just re-run the episode missions and such.
The TV show will continue too.
On May 10, 2013, Syfy renewed Defiance for a 13 episode second season to air in 2014. Reference: Wikipedia.
If the game is hurt, it will not be because of the lack of a show. Not for at least another year at least.