What happens when a listed rollercoaster gets too unsafe to ride? [Blackpool Pleasure Beach]

After hearing the news of the derailment of the Big Dipper (a Grade II listed 102-year-old rollercoaster) and Grand National becoming more and more unsafe with every passing season, what happens when these coasters become too unsafe to ride and retracking the whole ride becomes too costly?

Can a listed rollercoaster be demolished or can it still be SNBO indefinitely?