Yo DO-bro de Stringo:]
You don't want to get strung out on this one. Sometimes I let the drums fade out a song; it's an easy way to end because I don't have to have an extra hand to reach over and shut everything off at once.
So, if I have 8 or 9 bars of drums left over, all other tracks are done or faded except the drums, well, man, you can choose your own slide downhill to go out. Like Bruce said, depends on the tune and what effect you want to affect the listener.
As for fading into a song, haven't been there yet but it sounds like an effect for a tv commercial or some looney tune or a political speech.
Didn't mean to weave a blanket from a string.
Green Hornet