I'd say most of the remaining sky tips are safe for now as they tend to be around the old disused workings.
There are still a huge number of pristine tips out there in other countries, especially at the coal mines around Donetsk in eastern Ukraine- they are EVERYWHERE! I've put a link below to Google Maps where I've spent way too long looking at the hundreds of collieries in the area which I'd love to try and get to visit one day... https://www.google.com/maps/@47.9596103,37.5970904,2032m/data=!3m1!1e3