My dad, with Alzheimer’s, has stopped speaking out loud. Is it typical that he now only mouths words?

This happened with my MIL. She had a fall and lost a lot of cognitive function afterward. She was confined to bed and only spoke in whispers. No one knew why. She'd worn a hearing aid before this, but during her bed-bound years, no one knew how much she could hear. Didn't know how good her sight was, either. She could vocalize, though, because she occasionally had no problem telling her caregivers when they were doing something she didn't like! She lived to be almost 100.

What is unusual about this Christina is that it happened suddenly and with a fall that had a head injury.
I am truly relieved to hear that the CT scan was done, but I am not comforted that the ability for speech and the hearing was affected with this sudden accident.

As an old retired nurse, I would say that no, this is not normal.
Have you returned to the doctor?
How long has this change now sustained with your Dad back in his normal environment?
Are there any other changes?

I am concerned. I hope you will seek followup with a specialist and I hope you'll update us here. The best of luck out to you and your dad.

My Husband, diagnosed with Alzheimer's and I suspect he also had Vascular Dementia was non verbal the last probably 8 years of his "existence" (I hesitate to say his life)
Each person with dementia is different.
Different parts of the brain are effected and as you know different parts of the brain are responsible for different "tasks".
It is possible that the portion of his brain related to speech has been damaged.
You say he can no longer hear. Is this new since the fall or has this been progressing?
Has he had an ear exam? One of the BIG problems in some people is a build up of wax. I would have his ears checked and if necessary flushed. (It does make a difference even with a small amount of wax.
I am wondering if he is not speaking because he can not hear his own voice. (just a thought)

I would get the ears checked and if that checks out I would just accept that speaking is lost to the dementia.

You could request a speech therapist and see if working with a therapist might help.