Which would be interesting, seeing as how it was her father that heard Kate's question. ((Right before she went back to the precinct (on the day that Castle proposed), she asked her Dad, "What happens when the music stops? What if all we were in love with was the dance?"))
Does she repeat the question, or does Dad spill this to Rick?
It's very pretty, worded that way, but it's still a hope rather than a promise. It would be more romantic on his part (and more reassuring for her, I would have thought) if he wrote something like "Should the world fall silent, the dance will go on."
