[Stooky Bill]

As to why they don't have their own DR, I would hazard a guess they've done that as a cost saving. Usually this would be essential for a major broadcaster, but in STV's case it doesn't really make sense when they have ITV1 airing the same programmes most the time. So it makes sense to use ITV1 as DR rather than going to the huge expense of setting up a second playout operation.

There's two things getting a bit mixed up - DR and broadcast continuity. 

Last night wasn't a disaster, everything stayed powered and running. People left the building for a while and the only problem was continuing broadcasting. Which they did, with a combination of their existing automation, the ability of their staff to remotely access that automation, and the provision of a sister channel to be used instead. Looks like it all went to plan, textbook broadcast continuity.

If the worst had happened and the building had been badly damaged or rendered unusable then that's where disaster recovery plans kicks in. That's more than just what happens to the TV service, it's potentially everything to do with the company - from backups of data to relocating staff. 

STV, like any broadcaster will have both. Obviously I don't know what would happen to STV the channel in a DR scenario but my guess would be ITV providing the channel and one of their other studios doing the news. There'll be a range of options and scenarios planned for