Well, i don't think GF will let Tera go to another company, is still profitable with a peak of around 1000 players per day (steamchart), now if 50% of such playerbase leave or stop buying anything from the ingame shop i'm sure they will change perspective and listen.
Even if they let Tera go i'm pretty sure someone else will pick this title immediately, Tera still AAA mmorpg with a good combat system and pretty 3d models you can't really find in any other mmo actually released.
I guess i have to remember you that GF took tera NA, and this is the first American title (?) that gameforge takes so i guess no other company there was interested.
TERA might be cool but it's a sinking ship in terms of playerbase and even a good company couldn't do much imho after so many years of bad management. We also need to give credit about the fact that Bluehole is almost worse than Gameforge at developing their own game and they probably made more mistakes than GF.