With the split of the Liverpool-Norwich at Nottingham, EMR will have no presence at Sheffield except for the London trains. Giving them Hope Valley would be far more of an isolated outpost than it is for Northern, so probably still the first to be cancelled when someone is short of trains or crews. Operationally speaking the Sheffield service is an extension of the Manchester suburban network so it makes sense to keep it with the same operator. The issue with Northern may be that although they stable trains in Sheffield there is only space for a few and they have to go somewhere else for maintenance.
Northern Fail's operating area should be downsized. IMO, it would be logical and create more coherent operating areas to transfer the following services from Sheffield to the EM franchise:
Sheffield-Worksop-Lincoln/Gainsborough (& occasional to Cleethorpes)
Sheffield-Doncaster-Scunthorpe-Cleethorpes (with locals terminating at Scunthorpe)
Sheffield-Hope Valley and beyond (all services, fast and slow)
Sheffield-Nottingham and beyond (all services) and any extensions to Leeds
The remaining ex-GC suburban services in the SE of Greater Manchester (to Glossop and Marple Rose Hill) should be converted to Metrolink, with the Hope Valley locals run by EMT via Hyde to Piccadilly, together with M-F peak hour extras between New Mills Central and Piccadilly via Hyde.
Northern could extend its Macclesfield to Buxton replacement buses to Chinley, calling at Dove Holes and Chapel. This would also be useful for those evacuated from Whaley Bridge, some of whom are accommodated at Buxton. Slow, but much better than no public transport at all. It is patently untrue that road closures prevent replacement transport at these stations, as Northern has claimed.
Completely roundabout. It is much quicker by road from Chinley to Manchester via the M67 than via the Cat and Fiddle.