The Patriarch is pretty much a god so I guess he can make more dragon knights if he wanted to. Prehaps as you say future games could be based on more Dragon Knights created by the Partriarch I mean come on surley he can't sit on his a**e on his throne all his life doing nothing?
Also as Raze says some dragons might have fled to other parts of the world and could return later. It says you are the last one, yes but who's to know, there may be another continent on the world no-one knows about yet. Many possibilities.
