If Claus had been in charge when the portals opened:
Hour 1:
Claus is mid-speech about reclaiming lost territory when the sky rips open and synthetic war machines start dropping into Berlin. He immediately declares the Combine “Judeo-Bolshevik alien collaborators” and orders the Wehrmacht to charge them with bolt-action rifles and righteous fury.
Hour 2:
The first Strider appears. Claus becomes obsessed with it, calling it “a magnificent engine of will.” He tries to negotiate an alliance on the grounds that both he and the Combine clearly hate weakness. The Combine do not respond. They just keep stepping on things.
Hour 3:
All conventional forces are getting mulched. Claus refuses to authorize retreat because “the German spirit does not bend.” He does, however, authorize a new propaganda poster of himself riding a Hunter.
Hour 4–5:
Berlin is mostly rubble. Claus is in the bunker again (some habits die hard), screaming at generals that if they simply believed harder the pulse rifles would jam. Someone tries to explain overwatch and transhuman soldiers. Claus accuses them of defeatism and has them shot.
Hour 6:
The Combine offer the standard terms: unconditional surrender and permanent occupation. Claus’s counter-offer is that he becomes the Earth Administrator and gets to keep the mustache. The Combine drop a synth on the bunker.
Hour 7:
Earth falls on schedule. The only difference is that the residual resistance later finds a half-finished oil painting of a Strider with a little toothbrush mustache.
Gordon Freeman still has to deal with the same dystopia, except now the Civil Protection units occasionally quote
Mein Kampf for some reason and the propaganda screens have slightly more dramatic lighting.