I think in this scenario you have to go missed. Call me a wuss, but personally I would not want any part of those conditions (1200 rvr) unless I was ready to shoot a CAT II approach.
RANT
I got into this situation a few weeks ago actually, but maybe not quite as bad. Long story short a fog bank hit the airport when were about 30 miles out (reducing TDZ RVR to 1400), we whizzed through the CAT II monitored approach briefing on downwind and shot the approach.
Our monitored approach procedure has the FO flying coupled to the autopilot, so they alone are responsible for calling a missed approach if they don't hear the captain say "landing, I have the aircraft" before decision height. 100 ft above DH, the captain "goes heads up", removing himself from the instrument scan while searching for visual cues through the windshield. To me this is the ultimate act of faith in your fellow pilot. At those speeds and that close to the ground, I can't be looking outside very effectively if I have to worry about scanning the instruments too. I must trust that my FO is going to call the go around if we suddenly lose the signal, the autopilot goes into a funky mode, or he doesn't hear me say the magic words by DH.
It was a thin fog layer, so we could see the tip of the tower for most of the approach but never the ground, runway, or ALS. Complicating matters was the fact that runway was almost perfectly aligned with the sunrise (100 magnetic heading), rendering the approach lights virtually useless (washed out by the sun).
My FO, who came from a freight (C208) background, DIDN'T CALL MISSED after we got the "minimums, minimums" callout from the airplane and the RA dropped below 100.
Once we reached 100 on the RA, I sat there for a brief moment of contemplation before I spoke up and called the go around on my own (thank goodness for the aural warning unit). Of course by the time I had processed the thought of "hey he didn't call it, but we need to go missed" we had broken below the fog and could see the runway. At that point it was too late, I had already mentally comitted to the missed approach. Plus we were definitely out of position to land properly in the touchdown zone.
In the end we shot a quick missed. By the time we came back around the fog had started to dissapate and we landed successfully. I told my FO thanks for all the help, but don't be shy about calling the go around when we hit the minimums.
Moral of the story, just play it by the book, that way everyone is on the same page. If you're going to cheat the minimums, at least let the other guy know beforehand. I would like to know about it ahead of time so we can resolve the situation, rather than finding out at Decision height on a CAT II ILS. Maybe it's a little easier to cheat in a SAAB or 1900 when your going 100 knots or so but pushing 140 in an RJ the time from 100 ft to ground impact isn't long enough to d#ck around with IMHO.....
Later, over drinks, this FO informed me that there was "no way" he would've gone missed in those conditions in his caravan (which I can only assume wasn't even CAT II certified). I guess we can draw our own conclusions from that.
I don't post this to dig at freight guys, but I just hope we can recognize hazardous attitudes like this before they bite us in the ass. In the pax carrying world you have to remember that it's not only your butt on the line, but a whole bunch of other people are sitting behind you too. While this probably not the smartest thing to put out there on a public forum, I think it's worthwhile if anyone can learn something from this story.
/RANT
I've also had a situation coming in to a certain airport with triple paralells where approach would not grant my request for the runway with the best visibility, offering me either a runway with marginal vis or a hold at 3000 ft with an indefinite EFC.
So of course I continued for the runway with marginal vis (think it was 1900 rvr). I was not CAT II qualified at the time, and sure enough, on 7 or 8 mile final (just outside publisehd G/S intercept), RVR drops to 1600....go around....divert, sit on ground for 3 hours, good times.