ok so my headcanon for the “if you see finn, tell him…” scene has always been that Chewbacca replies “that you’ll see him soon.” because he knows Rey is coming back and he knows that Rey needs that reassurance too. She’s going to come back and she’s going to see Finn again. And it’s the perfect thing for both of them to hear, because Rey doesn’t know how to explain all of this, but the simple fact that they will see each other again is enough for both of them. That faith has been driving both of them, and at any time it is all they can promise each other and all they need to hear.