How about, as their way of giving us the Stone Cold Salute, "Last Song" by Edward Bear.
I'd also bet on "Closing Time", but wouldn't mind The Who's "Long Live Rock" if we're throwing out fantasy predictions.
To be over - Yes
If I had a choice to make as the last DLC, it doesn't have to be something poignant, just something epic:
Side 1 of Thick as a Brick by Jethro Tull-has all the instruments.
my personal choice although it doesn't have all instruments(but some could be faked)
Side 1 of Tubular Bells by Mike Oldfield
I'll settle for American Pie
"Hey Jude" by the Beatles :D why not right?
(before some anal nerd jumps at me I'll just be clear and say I'm joking...)