Actually, "death by fear" is already in the RPLHB; it's just not as likely as in your scenario. If you fail a Fear check by 16 or more you have to make a Horror check at the Fear check DC-5; if you fail the Horror check by 16 or more you may go into system shock (Fort save at the DC of the Horror check or take 3d6 Con damage), and must make a Madness check at the Horror check DC -5. That would take a heck of a Fear check and some bad luck, but a common or garden variety Ravenloft peasant could easily be frightened to death under these circumstances.