Here's what happens when a motor overheats. Not busting your chops, just letting you know. The pistons expand and eventually the rings drag on the cylinder walls enough to stop the engine. The engine will turn over again as soon as it cools, but the rings, because of their tight contact with the cylinder walls can lose their temper. This causes them to wear out more quickly, and you end up with a "smoker". There can also be scouring of the cylinder walls and premature failure of the crankshaft and rod bearings due to the excessive drag while in the process of seizing. The waterpump impeller can be replaced all right and will pump water and cool the engine, but the amount of damage done to the engine prior to repair is "iffy" at best. Sorry.