Lets start with a review of things revealed by the storyline so far:
- The Borealis is an Aperture Science research ship.
- Aperture Science is behind the portal gun in the game "Portal"
- It vanished mysteriously while in drydock and even a part of the drydock disappeared with it meaning it was either vaporized or teleported. Since Mossman did find the ship it must have been teleported - presumably by technology similar to the Portal gun.
- The ship is now located somewhere in the Arctic wastes.
- Chell was NOT located in the arctic wastes when she escaped from GLaDOS and so is unlikely to make an appearance in person.
- Eli was VERY concerned about the technology on the Borealis which makes sense as the Combine does not have any kind of local teleportation technology - yet.
- Even the teleport technology that Eli and the others from the resistance have developed requires a transmitter and receiver device to make a controlled teleport. The Aperture Science tech bypasses those requirements.
- Eli is now dead. Get over it already. He's gone.
- The superportal is now closed, but there are Advisors still on Earth who will likely begin working on establishing a new connection to the Combine homeworld.
- Kleiner's pet headcrab Heady is probably dead after having sneaked into the warhead of the missile. Though I doubt anyone but Kleiner will care about that.
- Despite appearances, the G-Man is not human. He has the ability not only to jump around in space, but to distort space and time. On at least a couple of occasions, he appears like a vision - visible only to Freeman (beginning of HL2 and Ep2 when the Vorts are healing Alyx).
- The G-Man and the Vorts do not share the same motives, but appear to have the Combine as a common enemy.
- The Vorts appear to be sincere in their alliance with humans while the G-Man seems to have someone else's interests in mind.
- The Advisors are more than just props in the game engine and in fact can be killed with some noclip action (you can even shoot them without noclip from the interior of the hangar before you step on the lift with Eli and Alyx as the wall they are hiding behind is not solid).
- This strongly suggests that at least one physical battle with the Advisors is in Gordon's future, but poses an interesting problem as they are very tough to kill and Gordon has always been totally defenseless against their powerful telekinesis.
- Dr Mossman's status is unknown. She may be at the Borealis or not and she may or may not be a captive of the Combine.
- The Combine have been to the Borealis including soldiers and hunters.
Now for my speculations and predictions:
- The game likely starts with Alyx and Gordon traveling to the Borealis in the helicopter.
- I'm sure they will bring some assistance. Barney, Dog and Vortigants are likely candidates.
- Perhaps the Vorts can shield Gordon from the telekinesis of the Advisors somehow.
- Before the chopper can reach the Borealis, it will be shot down with Gordon, Alyx and at least one of their helpers barely pulling themselves out of the wreckage.
- They'll find themselves on unstable cracked glacial wastes and will likely face headcrabs, zombies or whatever on the way on foot to the Borealis.
- Once there, they probably need to deal with a guard force of Combine stationed outside the ship.
- After they can make their way inside, they'll find some kind of evidence left by Dr Mossman revealing where to go next.
- The ship is booby-trapped which is the only reason that the Combine haven't already retrieved the technology they're after, but means Freeman and company have to watch their step and split up on occasion.
- At some point, they encounter the Portal gun and confiscate it, but instead of Gordon getting it, Alyx takes possession of it (after all, Gordon always gets to "have fun" with the gravity gun and now it's time for Alyx to get to play with cool tech). Besides that, it keeps the game from being "Portal 1.5". For a few brief moments, Alyx trades the Portal Gun with the gravity gun for some areas that need an HEV suit to get though and also need the portal gun. Once past such obstacles, Alyx gives the gravity gun back and takes back the portal gun (which she does use on occasion, but only when needed).
- Before locating the Borealis teleport technology, they probably have to defeat at least one advisor and Gordon will need to have some immunity or a way to cripple the advisor's telekinesis.
- They succeed at some point in destroying the Borealis and perhaps recovering the Portal gun in the process (using it to escape the explosion I bet).
- At that point most or all of the advisors still on Earth have converged on the Borealis and are killed in the explosion giving Earth a bit of relief from the Combine.
- This is the end of Gordon's role as a player-controlled character in the Half-Life series.
- Why? With the death of Eli and considering how much Gordon has done, he will be selected to take charge of the human resistance and another character will take the front-line in Half-Life 3 (Barney? Chell? Dog? Dr Kleiner? who knows).
- Not only that, He and Alyx will finally have a chance to explore their relationship and well... . They're almost certainly destined to be a couple.
- (edit) G-Man will most certainly make an appearance in this episode and we will learn more about who he (it?) is and what his purpose is in this whole mess.
- (edit) Perhaps we'll learn that G-Man is an agent of a force far more powerful and sinister than the Combine.
