My father (97) has dementia and spends several hours a day sleeping in his wheelchair. Is it possible that he can lose the ability to walk?

Yes. It is possible. Bone and muscle mass diminish quickly in the elderly and the lack of drive to exercise means law of drive to eat. Just no appetite, and sleeping is the thing they love. As my dad said shortly before his death at 96, he could sleep all day and wished he could just sleep forever. Hard for us to imagine, but it does happen. Are you caring for your Dad? Will his lack of mobility hurt you directly? Encourage all of the independence you are able, but they still will do things their own ways. Be certain there is an excellent cushion for him to sit on, because bed sores are almost impossible to heal. The Back Store has a good one, though not inexpensive. I imagine medical stores would as well.

Yes it not only possible, but a given at some point. As the disease takes over more areas of the brain, the signals to operate various bodily functions are lost. Incontinence and swallowing and speaking go in that basket too.

Oh yeah, definitely.

Yes.

Yes, sitting in the wheelchair a lot will certainly impair your dad's walking abilities. (sitting makes joints & ligaments stiffer, & muscles weaker). Physical therapy cud get him back to safe walker use again.
It didn't take long for my mom to lose her leg strength once she used wheelchair (for only a week) after a minor fall. She was a hard worker too, always struggling to get back to her walker but to no avail. It makes me sad to tell that story, cuz it was the beginning of the end for her. Aging is awful.

My 92 year old mother has dementia and has lost her ability to walk.....not from the dementia, but from neuropathy in her legs and severe balance issues, especially after a stroke. I think dementia winds up stripping these poor souls of everything, eventually, although my mother can still eat a truck driver under the table. When I moved her into memory care and they asked what kinds of foods she enjoys, I said anything in LARGE portions...lol. They serve the residents on red plates which stimulates the appetites they often lose with the disease. Depending on the type of dementia they have, it can affect the autonomic nervous system which controls automatic functions like breathing and heartbeat, which ultimately kills them. As the disease strikes the central nervous system, lots of other functions and motor skills are lost as a result.
Best of luck with your dad, I know how tough it is to witness the decline of our once strong parents.