Its also a risk if they come out of the lav when you're pitching up for a dirty climb at TOGA power too, likely followed by immediate 30 degree turns and a fairly quick level off.

Asking them to stay in the lav until the plane comes to a stop makes a lot of sense but there is a 100% chance they will grab an ambulance chaser scum bag lawyer and sue for wrongful imprisionment and the lamestream media will run with it with extreme predjudice.

There is no one single absolute right answer on this. Either position is very defensibile in most cases. Either way that pax needs to be met by LE for disruptive behavior because they endangered others in addition to themselves because they couldn't hold it for one more minute?

Bottom line, whichever correct choice you make, defend it from a safety perspective. If pax up = automatic go-around then that needs to be in the manuals as a bolded memory item. It won't ever be of course, because that would be rediculous. Either way has risk, which was created by the passenger in question.