The mines were in financial trouble long before Thatcher and Scargill. Even before WW2 many of them were economically questionable. WW2 and the 50s delayed the inevitable, the process of closures increasing through the 60s with Wilson (along with the demise of steel and the railway network - Beechings 2nd report that really delivered the blow on the railways was in 1965).
Britain could not afford such loss making pits, steel or cars - our global competivity was shyte, management just as much to blame as the unions. I can remember starting work in a major British oil co and appalled at the number of sneior and middle execs plastered at 3pm and out of the office by 4.30, the last hour being devoted to the Times crossword and strong coffee.
At least Margaret got us back on the right tracks back in the early 80s, one other thing being arresting the brain and talent drain overnight - the slashing of income and unearned to back under 50% from as high as 98% on unearned.
Later on some of her policies like Poll Tax (though philosophically good) and Hong Kong were skewed and her listening skills gradually deteriorating as she became demagogic - a bit like Tony B did as well - that goes with the turf, I believe, and is a good reason for a maximum of two terms in power being brought in.