We would be screwed, or we can just crowbar the hell out of it.
Here's my theory: The only way a zombie can latch on to someone is if their head's exposed, right? Well, say Gordon was headcrabbed with no head protection, and then this "Zordon" found the HEV faceplate/helmet. The headcrab would be completely protected, and assuming that the Suit was fully charged with maximum health, Zordon would be completely unstoppable, as we all know how good Freeman is with guns, and we know from Episode One that Zombies can use weapons (case in point, Zombines) , so I don't think anyone would get near enough to Zordon to "crowbar the hell" outta him. Anyone else see the mod forming in your heads? :D
Signed, BlackmesaExperimental [email: firstname.lastname@example.org - in case anyone has an idea for the aforementioned mod]