Alt-F4 isn't a "super uber process killswitch," but just the same as clicking the red X on a regular windowed program. Aces High doesn't just die, it enters the same closing sequence as when you click Quit on the splash screen. The only differences being that is saves your currently recording film and, if you're in the middle of a sortie, "crashes" you (not program wise; as in, "You have crashed," adds a crash to your score page, makes the Scenario logs look funny if you're in a ship gun...).
I remember waaay back in Aces High I, someone claimed that using Alt-F4 corrupted your textures and cache. In the however many years I've been playing, I've had to clear my cache twice, and that's easily attributed to other causes.
