re: My elderly next door neighbor died from a heart attack in his driveway this AM.

Sadly the dog will probably mourn himself to death.
Dad had a cousin that died very young and his dog jumped into the hearse at the church. The funeral director moved to get him out but decided getting bit wasn’t worth the effort. That dog died at his masters grave never leaving or eating the food he was brought.
Hard to describe that kind of bond.
Sorry for your loss Lonnie