Had this happen a couple of years ago going DEN-NRT-BKK. Mechanical delay leaving Denver and missed the connections that night in Narita. We (quite a few people) were put on a Thai flight that went from Haneda to Bangkok that left very early in the morning. (Bused from Narita to Haneda in the middle of the night.) I thought the UA staff in Narita did an excellent job handling a tough situation. So, technically rebooked the next day. I also think there are ANA flights from Haneda to BKK in the very early morning hours. As many have said on this board, best thing to do is be aware of all the options that are available to you.