A Nydus worm burrows out of the ground. It spawns a constant wave of Ultralisk, Zerglings, Infestors, and Hydralisks that massacre the bio-ball berserk swag troopers.
The dead Melon, Indreams, and Redroach become infested terrans and are given a choice to press the button or not.
Indreams, completely integrated into the hive mind of Sarah Kerrigan, does not have free will and cannot press the button.
Melon and Redroach still retain their free will, but they don't have much time.
The red button is not pressed yet.