Stalled vehicles must be off (towed if necessary) the highway, not partially on, to ensure the safety of other drivers. That's true of major highways in most countries.
A mechanic stopped to see if they needed help. That was an opportunity to ask the mechanic to either help, or call a tow truck (if cell service was unavailable). I understand that the couple expected that the van would cool off and be good to go, but that didn't happen if they were there from 3:20 until the evening. It's very unfortunate.