If I remember correctly, the cave doesn't have a stream running into it and flooding would seem unlikely. An interesting page here on the top notch site peak district caving info.
No! The most hazardous part is the potential for slipping on the autumn leaf fall on the way back down the access paths. It gets 'damp', as in a few trickles from the roof and the odd minor flow down the main passage. There isn't any stream in the system.
There is a duck near the bottom that leads into a lower section still, and I'm sure there is a 'sump' at the very bottom, but only in the sense of a water-collection hole rather than diveable passage, but it is very high up so it's well-drained naturally really. I'm sure some ancient sough was responsible for keeping it all dry - most likely Wragg Sough, started in 1680. The history, geology and archaeology of the workings along Coalpit Rake are discussed at length (with a modern survey) in the PDMHS Bulletin 'Metal Mines Through Time', Vol 17, No.3.