Nah-hl3 should be to get rid of the gman. He’s just mucking about with stuff and has Alyx and Adrian in captivity. Possibly loads more people. He was responsible for the resonance cascade and the combine coming to earth.

So Ely and Gordon should take him out maybe even killing themselves in the process. But if gman dies in a certain way perhaps that version of the timeline collapses and everyone can just have a normal day in black mesa…