Sam and Diane dance to what song?

Factual Questions
1

In the Cheers episode when Diane leaves (“I Do and Adieu”), we see Sam and Diane as an old married couple dancing to a piano song.

What is the name of that song?

2

Irving Berlin’s “What’ll I Do” according to Mrs. Blue Sky.

Here’s the lyrics

3

Thanks.

That was one of those things I had always wondered about but only just now remembered again and realized that I could find the answer with Google and/or Straight Dope.