It looks like UAL804 is indeed in the air now heading to SFO.

One of the things about the ultra long haul flights like this one is that there is a very short window to play with in terms of crew duty times, and an extended delay like this one can put the crew beyond the limits they can legally fly. The stop at SFO to recrew the flight was a creative way to avoid having to cancel and have everyone stuck there for likely an extra day.