Here's a scenario I had not long ago
Short final into DCA and aircraft is fully configured. FA calls up and says someone just went into the lav.
What do you do? We did a go around but I'm not so sure it was safer than just landing.
I had this scenario with a twist a couple years ago. I was the captain, and we did go-around. But it wasn't at DCA, and we were way early with plenty of fuel, and there was a little more to it.
We were flying DTW-IAH. There is a large cancer treatment center in Houston.
A dad and his son of age ~14 were in first class, first row.
We didn't hear from the flight attendants until about halfway through the three hour flight, that the son had been in the forward lav for about a third of the flight so far, off and on over a bunch of times. They figured he was airsick or ate something bad the first time or two but then inquired and the dad told them he was on the way to another round of cancer treatments for colorectal cancer. He apologized to the F/As and said there hadn't been any trouble like this on the flight the week before nor did he anticipate this before the flight. They were sympathetic to his situation and said don't worry about it. They ended up closing off the lav for everyone else for the last hour.
I got up to hit the bathroom before descent and saw that the kid was sound asleep. We reiterated to the F/As, who were fortunately vastly experienced from past lives at a defunct airline, to just call us and use their best judgement if he wakes up before landing and is back in the lav again towards the end of the flight.
We were something like 30-40 minutes early and had tons of gas, so we briefed that we'd break off the approach and come back around if we had to, but only once given the fact that the kid and his dad knew exactly what the rules are but he was just not able to control himself.
IAH was really quiet on approach and it was clear and a million so we stuck with the plan. We don't practice go-arounds often enough anyway, right?
Sure enough, they call us at 2000'AGL on the glideslope and say he just went in the lav. We told them, if we don't hear from you by the time we're at our decision point, we'll assume he's still in there and we'll go-around. We told them 'our decision point' but we had briefed we'd give it until 500' AGL or so, after telling tower we might need to climb out and we had their instructions all set up in the FMA ready to go so it was very benign.
We were back around in five minutes and on the ground. He looked real weak and tired walking off, understandably, and I think most passengers in the first half of the jet kinda figured out what was going on and so we had kept the post-go-around P.A. extremely basic and certainly the opposite of the chastising, rude announcements that single one passenger out without knowing one iota about why they got up. I hate that; obviously in our case we didn't even need to ask the passenger to sit back down because he very well already knew that.
I recall the four of us talked about it at dinner that night and figured we did everything about right given the slightly different circumstances.
My rationale with where to draw the line for going around was the point that we must be on a stabilized approach and spooled up and on speed. I figure if we're permitted by the book to get that far and find ourselves out of the parameters, then a "no fault, mandatory" go-around from there must not be that big of a deal. Now, if the F/As had called us at 100'AGL, well first of all we knew they knew not to, but if they had, we'd just go ahead and land it.
Hopefully the kid's attitude+modern medicine let him kick cancer's butt.