The status of Half Life 3 might be a mystery to the fans but not its plot. After 10 years of non-stop waiting for the game, fans must have a pretty great idea on the events that will be happening in Half Life 3.
With strong references to Half Life 2 and the fan-made Half Life film, Half Life 3 will start with the Combine, gaining full ownership of the most-sought after weapon in the universe, the Borealis. The alien race will then study the Borealis and eventually, get it to work.
On the other hand, the Combine’s goals will be met with a resistance, which is the protagonist. Of course, the main character will be aided by both Alyx and the G-Man as they attempt to destroy the Borealis once and for all.
After a lot of battles and encounters with the Combine, the protagonist will finally obtain the Borealis in time to destroy it. Once done, the Combine will result to a full retreat, thus, restoring the peace.
Obviously, there will be some deaths to key characters in Half Life 3. There is a chance for it to be the G-Man. Regardless of the character, death is important to complete the Half Life series once and for all. Otherwise, it will be anti-climactic.
As likely as the above sounds, the odds for Valve to produce something similar are slim. After all, the expectations for Half Life 3 are high and Valve wish to meet the fans demand with their own set of ideas.