Mom 88 w/ dementia her tongue is white and she is sleeping all night almost all day is this a sign of final stages?

As a speech therapist that worked in nursing homes for many years, I would first have a physician make sure it isn’t thrush or anything similar. If you allow the film to remain, sometimes it can build up, and their tongue can become cracked and bleed. It is usually dried saliva. We used toothettes dipped in warm water and wiped frequently over several days. Do not use toothettes if a person bites down as the sponge end could end up blocking their airway. Ask nursing also, they have a lot of strategies to deal with this. It is very common. Good oral care and wiping out their oral cavity can help.
Also, without good oral cares, the bacteria can colonize and cause aspiration pneumonia if it gets into their lungs while sleeping.
When cleaning their tongue and mouth, make sure their bed is upright so they don’t choke.

No one can predict when someone will pass. There are signs when the end is near; sleeping all the time, not eating, sometimes people start talking to relatives who’ve passed.

If Mom isn’t on Hospice, do you think you should ask for it? It makes things easier for everyone. As for cleaning her tongue, I might call her doctor to see if anything truly needs to be done. Do you think she’s in pain because of it? Trying to do anything about it could be very unpleasant for her and cause her to gag. I’d check with the doctor first.