WHAT HAPPENS TO THE ENGINE AND GAME DATA?
Nothing. Yes, that’s right.
Why nothing? You have to understand how licensing works.
A person (or other legal entity, such as a company) creates something (code, artwork, etc.) In most countries, the creator automatically becomes the copyright holder. You can also aquire the copyright from the holder (presumably that’s what Illfonic did).
The creator has full rights to the stuff they created, and other people have none. So, in order for other people to be able to do anything with that stuff, the creator gives them a license which allows them to do certain things.
The creator can give how many licenses he wants, and they can be different licenses for different people.
In this case, Alien Trap and ID Software already gave the world at large the Dark Places engine under the GPL license. Then they also issued another license (or transferred copyright ownership altogether, which would mean they stop being the holders) to Illfonic.
But the interesting thing is that copies of the stuff that was already distributed under GPL cannot be “recalled”. You cannot go back and say that you want all those copies destroyed, returned, require people to stop using them or developing them etc. Same goes for the game data.
Basically, there’s absolutely nothing anybody can do to stop the community from picking up from the last official release of Dark Engines and the release of the game data and keep on going.
Look at it like this. Nexuiz, as you all know and love it, is now twins. One brother goes to live with uncle Illfonic and one stays at home. They both start from the same place. They are identical. But they will evolve in different ways in the future. How — that depends on you, the community, vs Illfonic. Each party will take their twin in a different direction.
You haven’t lost anything. Illfonic cannot take anything from you. If their game becomes a success and yours dissapears it will be mainly because of what you do, not about what they do. Here’s hoping they both will do great.