On the WCML and GWML (and probably other main lines) there is a well-developed "Plan B" at times of major disruption.
Things like cancelling the Tring terminators, the WLL service, one each of the 3 VTs to Birmingham/Manchester.
The GWML thins out services, with remaining trains calling at all main stations.
WMT turn one of the Birmingham-Liverpools at Crewe, etc, etc.
It seems clear that Northern and TPE don't have such an emergency timetable, or they would have implemented it.
Something like reducing 2tph to 1tph throughout the system, or turning certain routes short with remaining trains filling in.
Seems a glaring omission to have to go for random cancellations rather than switch to a planned lower frequency throughout.
The impression I get is that Northern's scheduling of services (stock and crews) is so complex and interdependent it cannot be unpicked in this way.
As discussed on one of the (many!) other threads about the changes/ problems in the north of England, the service patterns in the north west are to blame.
For example, before the changes, you had two trains an hour from Blackpool to Manchester and two trains an hour from Southport to Manchester. But instead of a simple half hourly service on both routes (which would therefore cope with disruption and be relatively simple to reduce to hourly) both Blackpool and Southport had one train per hour to Manchester Airport (via Piccadilly) and one train per hour to Victoria. Same with the Eccles line (some services to Pic, some to Vic).
Unfortunately the new franchise continues this complicated set up - e.g. the Calder Valley is to have an hourly Southport service, an hourly Chester service and an hourly Manchester Airport service. If all Calder Valley trains ran through to Wigan/ Southport then it'd be simpler to reduce the frequency and drop one or two trains per hour.
Nine trains per hour from Piccadilly to the Airport but a *seventeen* minute gap each hour between xx:33 and xx:50 because the nine trains are all from different places so are badly split apart.
When you have a simple half hourly service (as West Yorkshire does on most routes), going down to hourly can be acceptable. But when you have lots of separate hourly services, reducing them to every two hours will create some huge gaps.
But, in fairness to Northern, the paymasters want to have lots of direct hourly services, everywhere wants a direct Piccadilly service (rather than half hourly to Victoria), MPs and Councillors will demand a direct Airport train, there's people wanting various cross-Manchester services (e.g. Stockport to Bolton). So the whole timetable ends up in a giant mess where a butterfly flapping its wings in Southport can mean delays at Alderley Edge for the rest of the day.
About the only bit working reasonably well seems to have been the lines to Glossop/ New Mills/ Marple, which are relatively self contained short/ simple/ half hourly services (with the exception of the bi-hourly extension to the Hope Valley) - so somewhere like Rose Hill Marple has an easy reliable service to Piccadilly every half hour, instead of having two badly-split hourly services just so that there's a direct train through to somewhere on the other side of Manchester. Keep It Simple...