Will the skyrim pc have single handedly killed all dragons or will there be a few for the next game?

Depends where the game is set, I would say. It's possible there'll be one as a big ol' "Boss Fight" but I doubt there will be random encounters.

There'll be no more dragons, just like how there was no Oblivion Gate ruins in Skyrim. They'll probably leave most aspects of the different quest lines out of the next game and start afresh again.