The hospital cannot discharge them unless they have suitable accommodation to go to that meets their needs, whether that be at home, a nursing home or whatever.
Their option would be to stay in hospital, you will get away with it for a while but the hospital will eventually apply long stay charges. Staying in hospital would be a very unreasonable approach to take though, as it is using a bed that others badly need. It is also very unfair on the patient who would have a much better quality of life in a nursing home.
Having some in hospital beds who only need nursing home care is part of the reason there are many sick people on trolleys etc in corridors.
Why would this person not want to avail of Fair Deal ?