IF there were to be a "zombie apocalypse" type catastrophe ... which power station type would last longest? Taking into account fuel, maintenance, and manpower needs. EG: Coal plants would go dark first, due to lack of fuel and manpower.

I would think that a solar power grid would last the longest. It has a unlimited power source and a lot of solar energy systems can even be automated and not require manpower. Maintenance would be minimal assuming only a few panels would be likely break, and the other panels would still run independently.