As a result of the strike, British Rail's annual coal tonnage fell from c.90 million tonnes the year before to 31 million tonnes during 1984. This at a time when BR were typically moving c.60 million tonnes of coal per annum to power stations. Oil usage in electricity generation increased significantly to partially plug the gap, and as noted above it also represented an excellent window of opportunity for the road hauliers.
The rail unions supported the miners by not crossing picket lines - this being at the time of the "Triple Alliance" of rail, coal and steel unions. Trains continued to be loaded at some Nottinghamshire collieries that continued working throughout the strike, their miners being part of a different union, and there still must surely have been a quantity of coal being shifted elsewhere to make up the 31 million tonne total.
Didcot Power Station, as one example, saw no coal trains for eleven months - the first train after the strike arriving on the night of 22nd/23rd January 1985. BR's coal tonnages never fully recovered, although they had been in gradual but long term decline since the late sixties at least - In 1985, 78 million tonnes were moved, with power station tonnages restored to around 60 million tonnes.
Many of the details above have been gleaned from "Merry-Go-Round on the Rails", written by David Monk-Steel.
Off topic, but it strikes me that even if it had managed to continue to eke out a living for a few years more, the miners strike would have sounded the deathknell for the Woodhead route anyway: I appreciate that it moved other traffic, too, but it relied in large part of movements of coal from the South Yorkshire coalfield to Fiddlers Ferry power station, a traffic already undermined before closure by the import of coal from Australia through Liverpool docks.