Rehab facility discharged my sister's boyfriend but the daughter won't let him go home. Medicare has stopped paying. Any advice?

We need more information to give relevant responses.

Has BF been living with his daughter? Her house or his? Was she caregiving for him? What is his impairment? Where does his daughter think he should be -- nursing home, assisted living, something like that? Why?

Is Medicare bowing out because he's used up all his days, or because he is no longer making progress in the rehab?

What does your sister want to have happen?

I assume his daughter has medical DPOA? Does her dad have dementia, incapacitated?
If not, he can make his own decision about what he wants to do. Who is paying?