King cross Northern line lift

While I am not 100% sure, I would be surprised if touching out and back in at different gatelines at Kings Cross as part of an interchange on a single journey resulted in two fares being charged. The system copes perfectly well with similar situations elsewhere where it charges only one fare (OSIs, Monument-Bank at street level, W&C at Waterloo, H&C-District at Paddington, etc).
Also, if able-bodied passengers got a free interchange but mobilty-impaired passengers had to pay then I think the Disabily Discrimination Act would have something to say.
It isn't very clear though when making an interchange like this that the price you see on the barrier on exiting your second leg is the cost for the whole journey, not the second leg, as you already got shown the price the first leg would cost if it were your whole journey when you complicated that. It might be more intuitive to show the additional cost (if any) at the end of the second leg, but this might lead people familiar with the current situation to think they're being charged less than they are.

(i.e. if your journey is A-B [OSI] C-D, and A-B costs £3 and A-D costs £3.50, you currently see £3 on the barrier display as you exit at B and £3.50 at D, leading some people to think their journey cost £6.50. If they changed it as above then you would see £3 exiting at B and £0.50 exiting at D, but this may make people think that A-D cost 50p, who wouldn't be happy to have been charged £3 more than they were expecting.)

I don't know therefore what the answer is. (and sorry for digressing from your main question, which unfortunately I can't answer)

Diagram of lifts, taken by 21146: tinyurl.com/5u77ey7

WHERE has lift B GONE!!!!!!?

The lifts on LU are programmed to go to either a place of either relative safety or absolute safety if the fire control panel goes into evacuation mode. A place of absolute safety would be at street level and the place of relative safety would be a fire rated refuge.

These refuges are often achieved by a set of smoke doors that swing closed. Occasionally, and I'm not sure about the layout at Kings Cross but if there is insufficient room to install these smoke doors and therefore a room is used instead.

It is possible that level -2 is a refuge and the lift would go to this level in an evacuation.

I'll find out for you if this level has this use.

Regarding the gateline, the KX gatelines have an OSI set up between them so nobody should be charged extra going from one gateline to another and I seem to recall on this forum a few moons ago somebody being incorrectly charged as they exited one gateline, met somebody at KX mainline and then re-joined the tube through a different gateline and Oyster did not recognise the touch out/in as the end/ start of the journey but as an interchange.