Is it still running? Or were you able to get it to shut off?
Sounds like ignition has a broken return spring, or maybe the keyway stripped out.. It’s not too hard to change the entire ignition.. You can also remove the ignition cylinder and try to rotate the ignition internals with a flathead screwdriver. Basically, turn the key to ON, find the hole in the bottom of the column shroud, and stick something skinny in the hole like a long #1 Philips screwdriver. Or a mechanic’s pick. Push hard and that should release the cylinder allowing you to pull it out. This is step one for the ignition replacement as well, except to replace the ignition the shroud needs to come all the way off.
2000 E450 dually V10 wagon