Out of interest would the NC actually have enough staff - and I'm referring to producers as much as gallery staff here - at that time of night to leave the Ten without taking WN? If this really was such a problem, anyway, wouldn't they have sent London to Millbank (at least for the late bulletins) to ensure there was always a studio free at NBH? The fact they didn't says to me they don't regard what happened the other night as a particularly likely event.
Not really. There may be some staff around on breaks, or who are at the end of shifts. But you can't just fire up a tv studio without enough people to do it.
People have been going on about Salford being able to sustain the News Channel, but that's just a fantasy. They don't have the staffing, and they don't have the most recent content on their servers. The Salford operation is set up for what it does.
On the other hand, would there have been no technical way for the News Channel to have simulcast BBC Parliament, but with audio-only commentary from a correspondent
without
needing a full news gallery? And if they knew there was a chance the vote would overlap with the Ten, could they not have ensured there was a one-off back-up team at Millbank just in case?
You don't put anything to air, ever, without control over it. Your proposal of BBC Parliament pictures with audio commentary is almost what BBC Parliament actually do. But also, the routing of it would be incredibly hard, and not the sort of thing anyone with a brain would either suggest, or attempt.