It is generally true.
While the UK's tin mines can be opened and closed with the fluctuations of the price of the metal, coal mines are not so flexible. When a pit is shut, it generally remains shut.
Coal mines can sometimes be mothballed but generally, if men are not kept working to maintain the roadways etc, the mine will collapse (and in the case of workings in the North East, Scotland, and Kent (which were under the sea) will flood. The reason is geology. The coal is soft and lies in strata and mining removes great sheets of the coal with the areas behind the face allowed to collapse behind the workings. If the mine is not actively maintained or worked, these same collapses will happen on the face and the roadways.
One could -- at great cost -- sink a new shaft to get at the reserves (this has been done many times), but re-opening the closed mine is usually not possible.
Moreover, when the Coal Board closed mines, they typically filled them in with concrete (sometimes leaving valuable machinery below ground). This, of course, means that there is no chance of reopening only of digging new shafts.