I'm sure that you thought it would be self-evident
alf, but just in case there are others who didn't get the true picture... in Pans Ops, Circling MDA is not allowed to be lower than straight-in landing MDA. This isn't usually much of a problem with an ILS approach, but is often very relevant in a non-precision approach.
I believe the go around is always based on the initial approach.
The missed approach starts at the Missed Approach Point (or DA) for the specific procedure. If you have already started circling before losing visual reference, all bets are off. Regardless of anything else, every missed approach is based on a point (fix or DA) at the end of the
final segment of the approach procedure.
There's far too many possible variations in scenario as to the point at which you might lose visual reference during a circling procedure for me to try to detail any possible escape routes. And, of course, terrain (and/or other traffic) will always be a mitigating factor. The short answer can only be that, if in doubt upon reaching the MAPt., don't circle at all - go around.
You might be able to do better than that at an airport you know, but you are betting the lives of all on board.
There are LOTS of circling procedures in this country - they are, in fact, in the majority because a runway-aligned approach is often precluded by terrain. We also have many airports where circling is restricted to one side of the runway. It works here because everyone gets accustomed to it and develops a certain amount of rat-cunning that keeps everyone alive.
If your airline's training (and Sim refershers) does not place a lot of emphasis on circling, I'd suggest that you need to be sure that the existing weather will allow you to see all the obstacles so that you can circle safely - and comfortably.