When it comes to priorities in my life, FFXIV is pretty much the absolute bottom of the list. And if I have to leave a dungeon because my wife saw that we need to run to the grocery store before work, then I'm going to leave the dungeon. Because that's what responsible adults do.

Also, if you're in PF, the most time that gets wasted by someone leaving during a fight is exactly the amount of time you've spent in that fight. And if you haven't queued yet, zero time has been wasted. Not some giant chunk of time, as some people seem to be hinting at. And if you're farming, and they leave between fights, again zero time has been wasted.