FIL 88 with dementia/ Parkinson's 6 weeks post hip replacement surgery is leaving skilled rehab back to assisted living. Any advice on the transition?

Alicia I read your reply to me and this is what I have to say. The surgeon may want him to use a walker but what matters is the assessment of the physical therapist in charge of his rehab. When you have a care conference before discharge from rehab, most likely, from the way you describe things, he won’t be safe using a walker. It was hard to hear this about my dad too, and him being wheelchair bound required we move him to LTC because AL doesn’t have the staff to help him with all the transfers needed. Also, if you are his POA, then you have ultimate decision power as to what is best for your dad. Do not give your power away to the surgeon. If your dad is allowed back to AL and you let him, then is this in his best interests? Unless you get a caregiver to be there to help him you are possibly dooming him to break another hip.
he should not be using a rollator as yes they get ahead of them and they don’t set the brakes Mathis happened to my dad too. Better to use a regular walker. But still, he will need assistance. Ask rehab to attend one of his therapy sessions to see if he uses a walker WITHOUT assistance. I bet he can’t very well.

Just my experience with Mom.
She left Rehab using a wheelchair, was not to get up without assistance.
She had Dementia bad enough that she did not remember that she was not to get out of the wheelchair.  SO........After a meal and an hour of visiting, she got up managed to stand and promply fell and broke the other hip. 
The answer was a different facility.  The ALF's have different ratings.
The one she went back to had only an A rating and could not put a seat belt on her.  (No restraints) They have to have the choice to fall?!! Anyway, where she ended up they could do a loose belt ( to remind them not to get up,) with a Doctors written order!!!  This is important!!
The 2nd facility was also rated with a B  and possibly C rating. They took very good care of her there.  So be aware they can only do what they are allowed to do!!  This is in Montana.
Blessings on your Journey!

You say "You know there will be a fall soon as it is just part of the process." This seems like he should be in his wheelchair as mandatory for his Parkinson's.

I’m wondering why he is wheelchair bound. Is he never going to use a walker? Will they continue PT and OT using Home Health to enable walking?. I am surprised they are releasing him to AL as wheelchair bound. How will he get help when he needs it?

my dad broke his femur around his hip prosthesis, had surgery but could never bear weight and walk unassisted. He is wheelchair bound and AL would not allow him back. Hence he moved to LTC from rehab/SNF.

It is not IF but WHEN your dad falls again. I think having him in AL wilthout being ambulatory since you said he will get up out of the wheelchair, will doom him to fall. I’m sorry to say this but being realistic. You have good reason to be nervous. Find out what his Care Plan is before moving him back.

You think he will get better care at the AL? ALs can only do so much. If Dad thinks the rehab is a nursing home attached. Maybe it would be better now for him to be there. Private pay till money runs out and apply for Medicaid.

Try referring to the AL by NAME rather than as an abstract (ie "home"). I found with my friend who had moderate dementia that words like "home" had meant too many places in his 80+ years of living, whereas referring to his residence of 25 years by it's address made it clear where, exactly we were talking about. What is interesting is that even with moderate dementia, he was able to make certain emotion-based decisions (ie I explained to him that if he went back to his home of 25 years his situation would be exactly the same as when he'd left, with the same caregivers, after which he never ONCE asked to go back there. Hm.)

Just stay calm and keep reassuring him all is well. Let the people at his AL know your concerns. Put his favorite things within reach and call or visit until you are sure he is comfortable and settled back in. Deep breath!!!

Watch closely for hospital-induced delirium. Also with Parkinson's and Dementia combination, please research Lewy Body Dementia. Often this is misdiagnosed.

I'm wondering how long he's been gone from AL. He had a fall, needed a hip replacement, and then on to rehab so.....4 or 5 weeks? I also wonder how long he was in AL before he fell.

I don't think FIL going back to AL will be traumatic for him. Once he gets into his room and sees all of his things it will probably start coming back to him. It might be a good idea to have someone in the family be with him in the AL when he goes back. Someone who can stay with him for a while until it appears as if he is comfortable and familiar with his surroundings.