There was a lot of clamor for a new final line for Ben. I was never outright opposed to the idea, but I didn’t think it was worth the effort to find the right source audio.
Since you’ve already done that for us, I suppose this is back on the table. It could be something he says to her through the Force after fading away, or we could try to find a spot where you can’t see his mouth very well.
Personally, I’d like to make the “finish what his grandfather started” link more explicit. Saving the one he loves from certain death and all that.