My mother keeps saying she is going. She tells my dad she is coming to see him, and he passed several years ago. What can I do?

I guess the best is to roll along with what she says about your dad. Doesn't hurt anything if either she thinks she's talking to him or thinks she's dying soon. At 97, either scenario kind of makes sense.

I completely agree with not reminding her that dad is gone. Doesn't matter and can just cause her pain every time she hears it.

Dmvinson
I think I understood your post regarding your mom to mean that she is telling you she is about to die and that she is telling your dad that she is coming to visit him (as in heaven). Is that right?
Is she agitated when she says this or is it matter of fact? Not a problem if the later, if she is upset and crying then you might want to let her doctor know in case she needs something to calm her.
Of course we often think when we hear something like that, that the person may be depressed. But she may actually be looking forward to it and is just letting you know. If it’s a statement she keeps repeating and it bothers you then try redirecting her comments as Freq Flyer suggested. “Not today, Mom.
We have to get the laundry done. Here, you fold these towels.”
You don’t mention her health status. Has she been ill with Alz a long time? How old is she?
Since you didn’t pose your post as a question, we are just making assumptions. The more details you give us enables us to offer more beneficial suggestions to help.

dmvinson, what your Mom is doing is quite normal for a person who has Alzheimer's or Dementia. Let her continue to believe that she had spoken with your Dad and that she is planning on visiting. Don't tell Mom that Dad had passed, she will only grieve all over again.

When the time comes and Mom is ready to go visit Dad, now is a good time to pull out the "therapeutic fibs". Being it is winter, you can always use winter storms as a good excuse not to travel. You can also tell Mom "maybe tomorrow", chances are she will forget that you had said that.