Well, I'll probably get beat up on this, but IF the only damage seen is a clean hole knocked in the case, with NO accompanying cracks to the flange and gasket area, I'd VERY carefully and thoroughly clean the area around the crack, and cut some window screen to use as a patch - maybe several thicknesses, and use JB Weld to sandwich them together and secure them over the hole.
Naturally, if there IS a crack to the gasket area, all bets are off. And, odds are the dowel pin itself was either ejected thru the hole, or has settled in the bottom of the pan, where it will do no further harm - might even come out with an oil change...