Answered on the plot Discord, but putting it here if anyone else comes looking!

Full AUs still have some subconscious awareness of their Trench selves--that can come to the fore at player discretion--and can nudge them into helping out with the quest. We can jam about reasons AU'd individuals might want to seek out Illarion in-setting, so they can have a plausible gloss on what their real selves want them to do.