So digging through a Gmod add-on of the Half-Life 2 beta, I have found a map called Airex that i got interested in so here's my idea of how this might have played out. Basically I took 2 maps based around Airex and made a custom (or fan-made) chapter for the forever lost Half-Life 2 beta. Also includes Gmod posing to try to show the images of how it may look.
Part 1-
You would have entered the facility and stumbled upon a group of Resistance team members. You and the Resistance would be wearing gas mask due to the condition outside. They would have probably walked out of one of the buildings and now comes in Part 2.
Part 2-
They exit the building to try to activate some sort of machine to temporarily stop the Combine. They come across multiple Synth Soldiers and would have began fighting. While fighting, There might have been a Strider introduced to the game walking by. Time for Part 3.
Part 3-
After the battle, They would walk into a long corridor of halls with railings attached shooting at multiple Combine Soldiers. At one point, An Antlion Guard would have crawled up and murder one of the soldiers before leaving. The Resistance head out of the area after the blood bath and enter Part 4.
Part 4-
They walk through more halls shooting down Stalkers while seeing the Antlion guard head off to different parts of the place. Time for Part 5.
Part 5-
You get separated from your team and venture out into a big open area. While doing this, A Strider crawls over a wall and starts running towards you. Basically a claustrophobic fight. As you fight it, multiple Combine units will be entering the action. After the fight, You would have probably entered a control room after a short segment of killing off Stalkers and finally reaching a control room. Once you enter it, You would press a button activating a signal somewhere else to keep the combine away for at least 1 chapter or 2. Anyways this is the end. Leave a comment about if you think this could fit or not into the beta. ( use constructive criticism).