This falling-out was not fuelled by people visiting the mines who had not got NRW permission via the former CAL access scheme. People not using the scheme is not the fault of the scheme, and in any case nearly all the permitted mines were not in any way secured against unauthorised entry by NRW.
NRW told us it has simply become more risk averse because it gets many FOIRs from single-issue groups seemingly intent on demonstrating that NRW is not upholding the law to protect things of value to these groups. Bats were said to be top of that list. NRW maybe fears being held accountable in public and of being required to publish embarrassing FOIR answers about itself on its own website. And if a complaint got really serious then it might result in NRW decisions being Judicially Reviewed which exposes NRW to High Court scrutiny, pushing things up to a whole new level.
Now that NRW has killed off the permissive access scheme everyone is back at the status quo ante which is that explorers would have no choice but to visit without consent if they're intent on doing it. The need for consent to enter mines on government forestry land may not be obvious since walkers and cyclists and horse riders have 'unbridled' access to the same forests.
I don't imagine NRW is going to try to defend its territory and their staff are not allowed underground for H&S reasons. So interest would likely arise when people admitted to breaking forestry byelaws in their social media postings or magazine articles, or if rescue services became involved somewhere people should not have been, as per the back injury incident mentioned earlier.
Determined people will still venture underground, but now in more senses than one, they'll do the same things and visit the same places as formerly, and so from a conservation viewpoint having explicit permission or not seems to be neutral.
NRW scrapped a workable lawful access system created by explorers for explorers who wished to avail themselves of it, one that suited and managed modest levels of activity well and of which there has never been any criticism. They have thus left themselves with no rational basis for their opposite numbers in recreation to return to talk with them, and they also risk losing some general support too given the craven rationale for denying future access as we understand it.