Can HRC facility discharge senior that is ambulatory but unsafe to be alone due to dementia?

They cannot discharge him without a discharge plan that takes into account his ability to care for himself and without including his POA or next of kin in discharge planning. An unsafe discharge is just that and doing this would ding the license of the facility for certain. You need to get in touch at once with the social workers.

You tell them that he is an unsafe discharge. That with the Dementia he is 24/7 care and there is no one to supply the care or can he pay for it. If they want to discharge him its because Medicare has found he has hit his plateau.

Medicare pays the first 20 days 100%. The next 80 days 50%. Those 100 days are not guaranteed. If Medicare feels the person has hit a plateau and further PT will not help, then they are discharged. If they are 24/7 care and no one can care for him or he cannot afford care, then he needs to go to Longterm care with him paying for it or if he can't afford to pay, Medicaid is applied for.
Not sure if, as MacinCt said, Medicare will pay up to the 100 days if he cannot be discharged because its "unsafe". That is something I would confirm with the finance office.

@Cover999 He's in Central Florida.

Then you tell them this is an unsafe discharge unless someone wants to live with him 24/7 and have no life. Most of us will say not to take him in. All rehab centers use the loose term, ready for discharge hoping someone will take him so that they dont have to do paperwork for Medicaid. The next step is they can hold him for up to 100 days at a cost to him of $180 / day. After day 100 it increases to $350. This is the time to learn as quickly as you can, the limits of medical insurance and Medicare.