I also would class this under airmanship. Has the landing capability changed? I would suggest not - you've already pushed the big red button which has disconnected the geny. That's why the a/c is now Cat 3 single. On the basis the failure happened below 1000ft, then one has proceeded beyond the approach ban point, so presumably the quoted RVR's were sufficient. Any subsequent reduction in RVR is advisory only.
The only things that have changed are that the amber land asap has turned red, and you've already fired one of your bottles - so you've only got one left - so arguably less chance of extinguishing the fire if you take it back into the air.
I also would also be wary of adapting one's behaviour for the sim. Whilst I would expect critical discussion of the decision, I would feel a lot more comfortable defending the decision to override a small section of the QRH In a situation that I believe is outside its scope, than I would taking a red land asap back into the air with marginal odds of improving the situation. There can never be a paragraph, section or procedure for every eventuality or combination of failures.
It's got me thinking though - a more difficult decision, I think, would be about what to do if the required visual references were not achieved at the revised DH, with the fire still burning. What if we'd already fired the remaining bottle? For cat 3 single, this decision has to take place at 50ft above the ground.
Or alternatively - master warning CRC sounds at 1200ft. Latest quoted RVR's preclude cat 3 single approach. Fire still burning at 1000ft, the approach ban point. Continue or G/A? I can see it argued both ways... but I don't think the answer would be in the QRH...
Edit: sorry reptile - crossed posts. If it's on the live engine. then you really are in the poo - any thrust is good thrust. Hopefully it's enough to get you to the general vicinity of the runway.