Back in the late 90s and early 2000s, someone was working on his own “expansion pack” for HL1. It was a modification, but it was an ambitious mod which he intended to continue the story of the first game. I think Planet Half-Life used to host the site, but no longer. The plot of the mod assumes that you accepted the G-Man’s offer, and involves Gordon trying to deal with a terrorist organization which is kidnapping Black Mesa scientists and forcing them to open portals to Xen.
The concept was really cool, and there were already screenshots for all the chapters for the mod. The guy behind it was even interviewed about the mod, and I hoped that it would be able to be released around the time of OPPOSING FORCE. It never was released, and I tried searching for any traces of it with little success.
I think that mod was called HALF-LIFE: RESURRECTION, but it could have been another title. As I said before, I searched for it again, and although I found a “Resurrection” site for HL, it was for a whole bunch of unfinished mods unrelated to what I remember. Any HL veterans remember this mod?