If your correct regional news fails to appear, then no choice of substitute is necessarily ideal (depending on what region you're in, what size it is, and how many/few neighbouring regions it has).
Midlands Today might be the "best" failsafe for EMT viewers in e.g. Leicester*, but viewers in other parts of the EMT patch would variously find Look North (Leeds/Hull) or Look East (Cambridge) a better substitute.
(*But not so much when it's talking about news from e.g. Shropshire or Herefordshire though)
If Look North (Newcastle) failed to appear, then the substitute might as well be London News for all the difference it would make. Its utter irrelevance to the NE&Cumbria would not really be any worse than if Salford/Leeds/Hull (or even Glasgow!) was the designated substitute.
The only circumstance where a neighbouring region
be better than London/the NC would be if there was enough advance notice for a joint programme (incorporating some already-prepared reports from the failed region) could be organised.
Bristol has occasionally done "Points West & Spotlight" bulletins due to technical problems at Plymouth, incorporating the odd few Devon/Cornwall/Channel Islands news stories in the running order, and with a mega-pan-regional weather map.
I is well eloquent, innit.