Couldn’t you just cut Luke finishing the sentence on camera? Assuming of course that the new line is shorter than the original. That would give you more freedom.
But I see what you mean about not being able to extend the reaction shots.
Maybe the pause before “What are you most afraid of?” would be less necessary if you change the intonation so that the stress is on “you”. Then Luke would talk about HIS fears before asking Rey about HERS.