How do I approach my Mom that Dad passed away on Xmas morning?

It's natural for you to want to be the hero, but if you move her to another state, her health insurance company will have to change and if she is on Medicaid, she will have to reapply in the new state and may not get services for months. Have a long chat with her treatment team about what is best for her.

Yes they were in rehab together there will be nurse supervised social worker etc they were living with my sister she fed them nothing but muffins and milk took all phones etc I am just so sad I hope and pray she gets strong snuff to travel so I can take care of her after being abused so bad

Were they in rehab together?

Discuss it with her Dr and ask him to be with you
if you decide to tell your mom.

I don't think she will she is in rehab center and she knows they took him to hospital. But she asked me if I would take her there that was before he passed

She will pick up on your anxiety and try to comfort you without knowing why. Let her do that, let her have some control so she feels useful. If she says Dad went to dinner, just agree with her and assure her he's having a good time.
In her heart, she knows he is gone, but she may not want to verbalize that.

Were they living together? Maybe mom has dementia that she thinks he is fine and being taken to dinner. Why wouldn't they take her? That she accepts that is puzzling if she is competent. Somethingmore than general age related decline must be going on. Since you have not seen her in ten years I would expect you will see drastic decline from when you last saw her, especially if she has dementia.