Afraid of the answer.....

[911monty]

There is a possibility the residue in the tank is from the previous water pump. Did you see the removed pump? I don't think your WP saw high enough temps to melt or cause the impeller to fail since they are designed to operate in conditions to 220 deg. Once the system lost pressure steam is only ~212 deg. Yes the cylinders no doubt saw much higher temps but with no coolant transferring that heat, the entire block would have to be heated to the failure point of the impeller. If that had happened I don't think your engine would be running now. The caveat to this is, was there collateral damage to the pump when the alternator failed? Since the car appears to not be overheating while driving then the simplest step is bleed and drive again.
However if this was my car, in order to have any confidence in it, I'd pull the WP and check it's condition. if good, a new gasket and a new thermostat and you can have some confidence that your coolant circulating system is at least functional. If bad then the next steps can be considered to find the parts.