I was teaching my buddy the game Saturday night and for fun we started doing 1:1 dogfights (Luke/Vader, Solo/Fett, etc).

Had an interesting instance and I'm pretty happy with how we judged it, but I'm curious what you would've done.

Fett got a crit (Structural Damage) on Solo, dropping the Agility of the Falcon to "0".

Falcon was equipped with C-3PO.

We ruled that since Han was unable to roll defense due to having an Agility of "0", using 3PO's "Guessing" ability wouldn't play. (You can't guess what an unrolled die will come up as).

This made it even more interesting as Solo would still get 1 die when defending at R3, re-enabling 3PO's ability.

Correct. The same rules apply vs wedge or anything with outmanuever. No dice roll means c3po doesn't trigger.

That's correct, Threepio's card text makes it abundantly clear that if no dice are being rolled the ability fades out.

Excellent. Thanks!