My brother-in-law, retired airforce AP (E-8) and high ranking California Dept of Corrections official, was diagnosed with a non-operable and aggressive brain tumor. Dementia was an appropriate diagnosis. They put him in a nursing home but he left, several times, within an hour. They put him in a 'secure facility'. He left within a day... several times. He never got very far away. He didn't know where he was nor where he was going. He knew he didn't want to be confined and had the wherewithall to leave.
Eventually his oldest daughter took him in and he lived oblivious but happy until the tumor killed him.