In the discussion about a go-around from a circling approach, here's another view.
If visual reference is not achieved at the MDA then the go-around is that of the instrument approach just flown - easy enough so far. If the visual reference is lost in the circling procedure - same thing applies. This would probably be on one of those marginal kind of days we all just love!
However, and here's the difficult one, think about what you would do if the landing was baulked at a late stage, then the option to enter a visual circuit may well be the best you can hope for, traffic/ATC permitting.
All these eventualities of course were covered in your relevant and interactive briefing with your colleague!
Good preparation and planning are the keys to success for this tricky manoeuvre!