The Vortigaunt killed Frohman because he knew too much.
Why did the vortigaunt leave Frohman to die in the end of the series? Because he shoot them? They are not petty enough for that, besides, they saved Freeman, who has already killed who knows how many of them. Because he is a moron? No, we already know that Freeman himself is not much better. The obvious conclusion is the vortigaunt have been plotting the downfall of the human race all along, and Frohman knew it.
But, did they merely leave him to die? In Half-Life, people dont die when they have one point left, no matter what kind of amusing injuries left them in that state. No doubt it was the work of the vortigaunt. They have been plotting the death of Frohman for long, but in every ocasion there was some nearby humans and they had to keep appearances, even ocasionally saving his life, ironically enough.
- They saved Freeman because he was totally going to save the rest of the world later
- And second, Vortigaunts don't actually care about the fact that Freeman killed their kind as Death Is Cheap for them thanks to the Vortessence and that death was a way better option than enslavement by Nihilanth.
Concerned is canon in the Half-Life universe.
Hence, the Playstation Half-Life is non-canon. It will probably be alluded to in Episode 3.
- Well, that means we either meet Frohman, or we get an exchange along the lines of:
Generic Rebel 1: "The only thing that could make this situation worse would be if this whole thing was caused by cheese!"
Generic Rebel 2: "...then now would be a bad time to tell you about this guy I met back in City 17."
- Both have a similar style of humour and Mike and Dave would fit perfectly into Concerned's bureaucratic Combine.
The Vortigaunt left Frohman to die because they were aware he caused a lot of trouble
- Come on this one makes plenty of sense, they found out through his bragging somewhere that he caused a lot of the trouble and figured that this would help make the Combine easier to deal with.
Gordon Frohman briefly worked for Aperture Science
- In Portal 2, the overgrown potato diorama says that everyone had to do an experiment with a potato, because someone ordered too many potatoes. Even at the computers at Aperture had Keys that supposedly got stuck.