I've just been through similar with my DFIL.
And my own father has cognitive issues as well as a severe disability and has just spent 10 days in hospital with Covid.
It is a particularly worrying when anyone elderly, especially with Dementia or cognitive issues, to spend a while in hospital as they are prone to delirium in hospital.
So if you can do everything you can to counter that. In an ideal world, if one of you can be with him as much as possible whilst he's in hospital that would have the biggest impact on possible delirium and many other benefits obviously, but it's unlikely unless you are lucky and they are happy to put him in a side room (where visiting hours are MUCH more 'flexible'). If you can find the Matron In Charge of whichever ward he ends up in straight after the surgery and tug at her heart strings, explain his dementia etc, she might be able to make a side room happen.
Either way, ways to combat delirium are to orientate him as much as possible. So bring him a clock, a calendar, familair things, pillow/case that smells of home, famil photographs etc.
Does he have a phone? Is he able to use it & communicate via a phone?
My Dad can't as he's blind so it was a huge part of why we were allowed to stay with him.
If your Dad can, that's great, you can orient him regularly via the phone.
He will also most likely have a catherter, keep a close eye for any sign of UTI in hospital and when he comes home.
The second challenge is when he comes home.
Firstly the OT (occupational therapist) will want to come to your home and advise you on changes you need to make to make it possible.
If they have a house with different floors.. you'll want to start thinking about how you can make it possible for him to live on only one floor, as stairs will probably be out for a while.
This might mean, making a bedroom downstairs, getting a commode, putting grab rails and ramps around. I would start thinking about this now. The sooner you have things prepared, the sooner he can come home, if that's what you all want.
The other ongoing challenge once home is thaf My DFIL would forget about their new disability and try to get up all the time. Risking another fall (which did happen and put him back in hospital). So it became clear he required 24 hours 'eyes
On'.
This is pbviously completely exhausting for the entire family, esp equally elderly DMIL, so it soon became clear a full time carer was needed.
Sorry to bombard you but this is all fresh in my memory, and I was given lots of this advice/experience and it was really helpful at the time.
Your DF is 10 years younger than my DFIL so I'm sure the process & recovery will be simpler. It's so hard as you want them home as you know it's better for them on so many levels, especially if they have dementia, but equally, they will need a lot of care in the recovery process so if he goes to a specialist unit to recover, it will be easier on you as a family whilst you get things as organised at home as possible and it doesnt break you all.
I wish you all the best, and hope the surgery is successful.
With decent and REGULAR physio, he will he back on his feet. But do push for the physio as every day of it counts.