As with most of the content on that forum these days, it's nonsense. Likewise with the reasons why trains can't divert via Huddersfield.
Yes it's possible to electrify through Totley, Cowburn and Disley Tunnels but that's 3 long lengths of Victorian engineering and the cost is far higher per mile than, say, Hull - Selby. Which should be the cost effective priority between these two lines? Other comparisons are available.
TPE trains are diverted via Huddersfield as a matter of course. Via Penistone is not practical without more passing capacity or cancelling existing stopping services. If it were practical it would be done.
Diversion of the fast TPE services via Wakefield is relatively routine but adds almost half an hour to the normal TPE journey between Sheffield and Manchester, as it will on the next two Sundays.
EMR usually bus from Chesterfield and Sheffield to Stockport.
Northern may bus between New Mills Central and Sheffield - which takes for ever (1 hour 50 just for that section then change to train taking another 30 minutes plus connection time) and most who know will avoid.
A protracted blockade would decimate commuter traffic between the the two cities, add a further nail in the rail option from the east to Manchester Airport and severely damage the growing leisure market for the Hope Valley.
But don't be over concerned about passengers. How is limestone and cement traffic to be diverted?
My guess is that some bi-mode option is most likely. Electrify up to the Chinley end of Cowburn Tunnel and the Totley end of Totley Tunnel. Possibly electrify from Edale to Grindleford. The section from Sheffield through Dore up to Totley Tunnel would be a natural follow on from the MML scheme - as overrun it may be part of it.