The lengths of these tracks shouldn't matter, right? As long as they last until the end of the other tracks? Since the default for Post-Playback State on Activation Tracks seems to be Leave As Is.
Correct. The length I used in the video was long enough to keep these active on screen until we actually launched. As long as you don't have something after those tracks they'll stay active even after the animated sequence finishes. That's why both those tracks as the same length.
The smoke ring eventually dies off on it's own (the particles anyway) so it looks like it turns off naturally. The afterburner just loops, so as long as we enabled the particle effect it should play the whole way through afterward.