You kill him, go rest till the next day or night (depending on if you fought him in the day or night). Then go back in, kill the 3 npc's that have re-spawned there and wait for 10 seconds or so for him to show up again.
Uh... Ur dragon has no respawn time, IIRC. By looping Everfall once, you should be able to encounter it again. I'm currently farming it from the first town and I can fight it every time after I rest at the inn for one day.
You should be patient and wait for a bit. It'll eventually appear.