This happened to me just 3 days ago. Sailing to Subic Bay in the Philippines I overnighted in a little backwater and left the next day overheating. It was time to replace the impellor but could not get it out and only, like you, had the hub. I got a vice grip on it perpendicular to it and could not wiggle it off. Placed a large (1 1/2 foot) screwdriver through the hole between the impellor and the jaws then something on the waterpump to keep the tip from scratching and levered it right off. Had to return again to pick pieces of rubber out of heat exchanger.
good luck
good luck
