If it is completely embedded, and the magnet doesn't work, you could try pushing the blade to one side with a tooth pick point and sliding a piece of strong sticky tape into the gap , with the sticky side towards the blade, then put the toothpick on the opposite side and repeat. Then push the tape onto the blade using the toothpick to push the blade inside the housing. You should be able to overcome the resistance of the tumblers with enough adhesion. I just tested some kapton tape, it is not very sticky, but if you can get enough adhesion it should not break off, you don't want to use tape you can easily tear by hand.
Other methods using superglue or drilling and tapping the key, may leave debris in the barrel, so be very careful. Good luck