Hmm so this is why World News Today on iPlayer is showing the regular UK news?
Anyway, didn't something like this happen the other way round when Breakfast had problems some years ago and they switched the feed?
The building BBC Breakfast are based in at MediaCity was evacuated whilst they were on air one morning - before the 0757 regional opt I believe. I believe BBC Breakfast put BBC World to air while they were evacuated allowing them to easily regain control when they returned to the building.