The way Gamigo described the acquisition is they bought the assets, not the development teams. The employees left are basically running the titles in maintenance mode, if not on contract to show their day-to-day operations to Gamigo before they're laid off as well. 25 total staff are continuing on, with 200 laid off with no notice before the sale closed.
I wouldn't count on any of those titles developing further past where they currently are.
I agree that they will not develop past their current patches. And, I did read an article showing the layoffs and current staffing. My apologizes for not linking said article, but I thank you for bringing it up.
The reason I went down the road of "they will die soon" is that, for the average gamer (not all, just the average), a "maintenance-mode" MMO doesn't really last that long. Sure, the vast majority of private servers for games (WoW comes to mind) last quite a long time (using private servers as an example, since a lot don't update as frequently as retail servers), though admittedly, that happens because a lot of the end-game content is buggy and can't be played. The server devs have to debug and make it work. So, people stick around. A lot of the larger private servers have good dev teams and simply acquire the patches from live and make them work quickly.
However, games in "maintenance-mode" don't develop, or develop so slowly that there may not be new content for a year, or even more. So, the end-game becomes stagnant and the average gamer will get bored. Because, let's face it. You can only run that final end-game raid so many times before you get burned out and just toss your hands in the air saying, "Done!" and walk away.
Of the games that Gamigo acquired from Trion Worlds, i can probably see ArcheAge lasting the longest, since the end-game content for that is so heavily based on the RNG of getting the highest grade of gear to even get ready for said content. It will also likely be the biggest cash cow for Gamigo, since getting said gear requires items you get from the cash shop to improve your chances of good RNG for gear. Sure, you can get that stuff without spending RL money, but ArcheAge was never known for being non-P2W.
So, if I had to take a guess; Rift, Trove, Atlas Reactor, and Defiance will likely only last about 1 1/2 years, max. Maybe 2 if Gamigo plays their cards right. ArcheAge will probably last a little longer, but the stories I am hearing from people who use to play retail is that it's a ghost town (I play on ArcheRage, an ArcheAge private server). a lot of people from retail ArcheAge have fled to ArcheRage for bigger community numbers, and that fact it's running 3.0, which has been said to be vastly superior to retails 4.5.