I have boarded a plane a few times in the past and left for personal reasons. I got the miles and never thought anything about it. The flts left on time. I did not ask for a refund. These were business trips mainly LAX-SFO or LAS-SFO/DEN. I also did not care if I got the miles - but I did. These were on UA. I have also done the same thing on AS, AA and DL (all domestic). I think an International flt might be a huge difference.