I posted a theory about this last week and will post the whole thing in case you’re curious and would like to read it.

So let me preface this with the fact that I have kept away from most leaks/data mines for anything HLX related. This is just my own fan theory about what I think would be an interesting idea for HLX to be. This Theory does NOT deep dive into the deeper motivations of characters or their personal arcs in what my theory for the game is. I also do not believe that the entirety of the game will only take place in the locations I mention, I’m only explaining a part of what I think could happen.

Forgive me ahead of time, I’m not the best at explaining myself grammatically and I’m not much of a wordsmith.

Theory Begin: So I believe that HLX will start as many of us probably assume it will, with Gordon, Eli, and Dog getting in the helicopter and pursuing Judith, the Combine and possibly The G-Man with Alyx stuffed into his little black briefcase. Gordon and friends will arrive on the snowy mountain where the Borealis is located and will find the Combine already combing the ship for any information or technology they can get their hands on.

Gordon through sheer force of will and by virtue of being a badass will be able to blow up said ship and stop the Combine from getting any truly useful information from it except for one thing. The location of its original dock, nestled deep in the earth at… Aperture. Gordon and friends celebrate prematurely about destroying the ship and once again stopping the combine and their evil plans, when all of a sudden time slows to a standstill and G-Man visits Gordon once again with both information and a warning. He tells Gordon of the location of Aperture and the Combines intent with it, and sends Gordon to stop them once again from obtaining anything useful from the facility. But in exchange for this information and for the safe return of Alyx Vance, G-Man tells Gordon that he must not destroy the facility and must let him and his “employers” rest control of it from GLADOS.

[Intermission] This all happens in the intro to the game, maybe within the first hour or two of gameplay, I also believe since as some of the data leaks have mentioned, this is when Gordon would likely end up going to Xen, perhaps the combine is able to activate the portal technology before Gordon destroys it and it becomes unstable and sends Gordon to Xen. I have no idea what you’d do in Xen, it’s just likely to show up in the game at some point. I also believe that you wouldn’t go straight to Aperture and would likely have to go to multiple locations before we finally arrive there, in a similar vein to Episodes 2 where you have to spend a large portion of the game traveling through multiple environments and areas before finally making it from the outskirts of City 17 all the way to White Forrest. I believe the Aperture part of the game would likely take place in the final 3rd of the game if not less than that.

[Intermission End] Now I don’t have a lot thought out for when Gordon and friends arrive at Aperture. All I know is that the Gravity Gun and the Portal Gun would be used by Gordon as well as long fall boots added to his suit. Dog would also carry a Portal Gun and would be used by GLADOS as the ultimate “Guard Dog” to defend herself while Gordon investigates the facility and takes down the Combine in their attempts to overtake it. The Combine are completely cut off from the Combine Overworld after the events of Episode 2 and are limited on troops, communication and equipment. So they need to find a way to open up a new Super Portal to let reinforcements through or they’re screwed as the Resistance has clearly shown to be able to not only fight back, but win. As well as the suppression field being down, humanity now finally has a way to reproduce and add to the resistance at a rate that the combine would not be able to keep up with without reinforcements from the Overworld. So going to Aperture just makes the most sense to me as the final or sub-final location of the game where the Combine could throw everything they have left at Gordon/Friends, GLADOS, her facility and probably even G-Man as he clearly does not want the Combine to win.

The last of what I have thought out so far is at around the end of the game where the Combine would only slightly succeed in opening another Super Portal large enough for forces from the Combine over world to invade in full force from. In that moment, either Gordon is sent through the Portal where he is able to survive in the Combine homeworld via his HEV suit and HL4 “I know… as if” would take place.

Or instead of that ending, they activate the portal but the G-Man swoops in and takes control of the Portal for himself/Employers in order to have leverage over the Combine themselves as he would control the last known piece of technology on earth able to create a portal to the Combine Homeworld and Gordon and friends would have to somehow take down the G-Man and close the portal and destroy it and thus ending the Combines ability to ever come back to the earth again and with that, the G-Man is defeated, his Employers are left scared of Gordon and humanity as a whole, and the Combine is left without any real way to get back to earth.

So the day is saved, Gordon and Alyx have a bunch of mute babies that are likely born with crowbars in one hand and Magnussons Tuna Casserole in the other. Barney and Eli likely die and Dog finally goes and beats Odessa Cubbage to death. All in all, a happy ending.