If your water pump jammed up and immediately broke your timing belt, wouldn't the car stall right away? More likely, it caused it to jump a couple of rungs, and screwed your timing up something awful. Was there any noise involved? If the pistons crashed into your valves, or any other trauma sufficient to bend them had occurred, you'd have definitely heard it.
When you mention that you started to lose electrical power, was that from trying to start the car up again, or did stuff start to dim before it stalled?
ALWAYS get a second opinion when it comes to major engine distress.
