When you say the sprocket broke off, HOW, did it shear the teeth ? It is very difficult to tell exactly what has been damaged, it is possible that the engine stopped fast enough to prevent further damage, The trouble is making sure you don"t cause any further damage by turning the engine. This process takes some knowledge but I would first try to determine the cam relationships using the flats on the camshaft, if they are close, carefully line up the broken side with the other cam, you can then replace the parts needed just to turn the engine slowly by hand (all spark plugs out). You can then feel with a finger for pressure from each cylinder in the firing order. If all seems well, repair all of the affected components,and reset the timing properly. Get all of the broken pieces out of the way & change the engine oil!!!