Additional point.

Were there any seats left on the flight? If there are any standbys, the GA will put them on the flight when a ticketed passenger doesn’t show up in time. Then the flight may be full.

Once someone else gets your seat, it’s GONE, even if you do show up late but before the plane actually pushes out. (The only possible exception may be removing a nonrev space available traveler in favor of a paid one)