Network Rail is a UK organisation, and if it wishes, it could force the closure of lines for which the maintenance costs are prohibitive, whatever the devolved administrations (which are dependent on Westminster funding) wish to happen. The current Scottish government is mired in controversy, and Westminster has the power to suspend regional assemblies/parliaments if there is evidence of maladministration.
As for the S&C, it currently has 4 passenger trains per day each way and minimal freight. North of Blea Moor, there is just 1 daily freight train to/from Newbiggin Gypsum works and no through freight traffic in practice (although paths exist). The Arcow quarry could continue to be served as a siding from Settle Junction, with trains not needing to run north to reverse, and passenger trains could in theory continue to run to Settle, even if the line from Arcow Quarry to Carlisle was closed. If a cut-off was built from the Little North Western line to the WCML near Carnforth, express bimode passenger trains could be run from Leeds to Glasgow, calling at Oxenholme and Penrith (more useful destinations to serve than Kirkby Stephen and Appleby) as well as Keighley, Skipton, Giggleswick (for Settle), Carlisle and Motherwell. It is a very different situation now for the S&C than when the battle to retain it was fought in the 1980s, as coal traffic and other through freight trains have ceased. The line from Hellifield to Clitheroe Castle cement works is also in effect redundant to requirements.