My mother's aunt (my great aunt) went through dementia for years and we usually just went with the flow. GA was sometimes very funny. One time my parents were driving her and another great aunt (her sibling) to visit another sibling. They were driving from Pennsylvania to upstate New York. Dad is driving, GA in the front passenger seat, Mom and GA2 in the back seat. GA turned to Dad and said "What do you say you and me ditch those two birds and we go have some fun". Dad, very patiently, said "No, they have the gas money". GA went back to talking about something else.
When she passed, the priest at the funeral said something that stuck with me. He said "People say it is so sad that Edna had dementia. However, she was in a place where she was happy. She didn't know about the 9/11 attacks, she didn't know if friends or family were having money troubles, she didn't know about other world events. She was happy and that's enough.".