I grew up in Kimberworth, Rotherham during the mid 60's-late 70's, and my life after six years old was defined by the shale spoil heaps from the opencast mining. They were fabulous - complex bike-tracks (years before BMX), sledging and skateboarding venues and just good places to sit on top of in the summer, as they were so high. They were all grassed-over and never really hampered my teenage development in any way.
When the council landscaped them, we were devastated, and even sabotage of the diggers was meekly entertained in protest, though we were only fourteen, so out and out wrecking wasn't really feasible. I don't remember any locals preventing their kids from playing on them.
A lot of this sounds like hot air, to be honest, and I'd hope the mine would go ahead. This place isn't just for looking at...