Cancel? They're in SFO trying to get back Houston. They can change - but what to? A 764 is still going to be the best ride back to Houston from SFO (it looks like tomorrow's 787 might also be changed out) unless they can find alternate routing. But by now, the forward seats on any 787 they can get to have probably been taken one way or another. Just get on the plane and go home. Try another time.