I just saw this film again and one thing stood out to me this time - at least three times in the first half of the film a character says something along the lines of ‘if we fail, it was all for nothing’. It gets rather tiresome, and the final time this happens is with C-3PO before he is mind wiped. I think a far stronger version of the scene would be to simply mute his dialogue, so he would walk away from the group in silence. Poe would ask what he was doing, and only then would he reveal his decision.
Yes, I really love this idea. Having a quiet moment with the “talkative droid” would be pretty effective I think. It makes the moment more serious if 3PO is silently thinking it over.