Rather than absolute winning or losing tunes, I'd rather have short musical stings when a friendly or enemy plane goes down. Again, not so easy to implement.
That's actually what I meant by "phrase" (sorry, I didn't explain what "phrase" means in musical terminology, it refers to short groups of measures, kinda like words are grouped into a sentence, and they are typically repeated).
From the composing / recording end, it would be easy to break up a track into phrases or segments, although for the coders, they would have to make the game keep track of playing a set order or sequence of such segments in an order that can change when an aircraft goes down (for example, a UFO goes down, and a "happy" or "victory" segment comes up next before returning to the main sequence) and it would get complicated quickly. On the other hand, if all that work was done, yes it would be very cool, dynamic music that responds to what happens in the game.
And an update: I actually got a "rough draft" track uploaded to my website server, although I'm not fully confident it would work:
http://www.destructavator.com/public/ERc1g.oggThe guitars need work as I only did quick, rough takes and was also making up the tune while I was playing it. It certainly isn't a finished product, but if anyone likes even part of it, I can bring out and develop that part and axe the rest.
This track is just one of several ideas - I'm working on some others that have a different mood and feel.
Again, I'm not completely happy with this one, although on the plus side it's very loop-able in playback.
This particular track was made with the "glory/off-to-battle/save-the-day" type of idea when I started it.