While not a 6502, 6809E chips fail on the Coco quite often. The cartridge connector is
directly connected to the processor without buffering or protection of any kind. Removing
a cartridge, or jostling the disk controller cartridge with the power on can short lines
and kill the chip.
Cloud9 sells a board that one can install with a 6809E or the Hitachi version of the 6809
(6309) to protect the processor.
http://www.frontiernet.net/~mmarlette/Cloud-9/Hardware/Pro-TectorPlus.html
I haven't bought one yet, because I bought 68B09E chips from Jameco for $5 each.
I've only seen one Coco with a blown chip, and I got it that way.
Al