I have had one solenoid failure on the start side, resulting in a closed solenoid, therefore no fuel flow. One solder joint on one wire had failed. Resoldered wire and all was well. This would seem to indicate that a solenoid fails in a closed position.
Jerry
You are correct that a fuel solenoid will always fail in the closed position,
IF it is an electrical failure. A mechanical failure can be either open or closed. A mechanical failure could be many things, a broken spring that no longer closes the valve, a piece of dirt/debris holding the valve open, the valve seat wearing out or many other things that would be very unlikely.