I've found it occasionally inconsistent. It will disappear on me at odd times, but generally only when I'm offline. Being online in the app seems to help it re-appear.

On the other hand, I've also had it not disappear by itself hours after a flight. Manually swiping it away doesn't always guarantee it stays gone either. Probably just an artifact of it being a work in progress. In general, I've been quite pleased with the effort and I appreciate the info in the Dynamic Island when I'm otherwise using my phone. It's distinctly more informative than having to bring up the app. And it was also through the Live Activities that I learned I had been upgraded on a recent flight to Premium Plus after I had boarded the aircraft.