Hello
@Ziggy Starshine and welcome to DTP, although I am sorry that you have found us at this point.
I notice that you have posted this under "End of Life Care". Has your OHs mother been confirmed as being at End of Life? As she is in a care home I assume that she has been checked for things like infections. I do think it would be a good idea for your OH to have a very open and candid talk with her mothers GP about what he thinks and expects.
Apologies if this is premature and she is not at end of life
When someone dies from dementia their body shuts down slowly over days and weeks and they stop eating and drinking as part of this process. Many people are concerned that they are starving to death, but that it not true - they are already dying and their body no longer needs food, so that is why they stop eating.
The doctors will give painkillers and other drugs to make sure that they are pain-free and comfortable. Usually this is by injection, patches or, in the last days, by a syringe driver. Relatives can help keep them comfortable by using little brushes or sponges to keep their mouth moist once they stop drinking and can put moisturiser on their dry skin. Hearing is the last thing to go, so make sure the important things are said - I love you, thank you, please forgive me and and (if appropriate) I forgive you.
You can also read to them, talk to them and play their favourite music.