Step-mom may be moving five hours or more away from my 92-year-old dad who has Alzheimer's, dementia and Parkinson's disease. Is this still a marriage?

Dad is living in a nursing home. Step-mom is 88, has cancer and some mild mental decline, renting a condo about 15 minutes away because she insists she is not ready for assisted living. A couple of weeks ago, she indicated she now wears dark glasses when she drives during the day and never drives at night, she said if she ever lost the ability to drive she'd move near one of her children which is at least five hours away. I understand she'd probably prefer to have one of her kids care for her than assisted living, but what does this mean for Dad's marriage? Not to put too fine a point on it, but her assets (she owns a small apartment building in California and gets a monthly stipend, and she also sold her own home a couple of years ago) are one of the reason Dad's not on Medicaid.