It's all sewn up nicely, there is the rule, something like not walked in x years, but the people campaigning to re open them will make sure they have evidence of walking the 'path' and that it must be re opened!
Was talking to my local councillor, and a few years ago the same happened on his land, that path had been officially closed due to a river straightening or something, either way the crowd from the 'ramblers society' have plenty of ex lawyers and whatever and they ran rings around the closure and had it re opened!
By rights there should be some form of survey to see if such expenditure is worth it, but it doesn't happen!