Payment card networks have delegated authorization plans, where if a major processor goes down, they will still route transactions and use a simplified secondary network for making approval decisions.
It's called "stand-in processing", and I assume it's the inspiration here.
The Monzo example feels different though, as they're explicitly not looking to replicate all functionality, just something minimal to get by whilst they fix the primary cloud services.
Monzo were the first bank here to run entirely on the cloud, so I imagine the regulators were extra strict with them.
I'm not saying this level of resilience is due to that alone, but perhaps it started them on the path?