Last year I was on a 78(8 or 9, don't recall) from YVR-PVG. We had a 2 hour delay while they fixed the port side lavs. They told us that regulations would not allow them to take-off because there is a defined ratio of working lavs to pax.

I have no specific data on what the numbers are so this post isn't that helpful except to say that the outcome for me was different AND it seems the Dreamliner has a flaw in this regard.