I think the entrances already were bulldozed with soil many years ago when the mine shut (about 1965) as you only have a narrow gap and then slide a down a short slope inside. The grilled entrance had soil dumped over it earlier this year and thats already crumbled away significantly (thats the one in above picture where you can see daylight shining through).
I was watching a youtube video of an old mine in USA being explored and the bloke said at one point that the echo of his voice was becoming muffled, thats apparently a sign of rotten, unstable rock and I must say that sound in Cults just falls dead, theres no echo at all in most places in there. Theres a lot of waste/deads in there also though, that must soak up echoes quite a bit, but one glance at the roof in there tells you its seen better days, most ceiling rock is cracked and fractured to hell in there and theres bits of roof the size of a compact car have come down in places.