The bolts have done exactly as designed, broken rather than the boat when the rudder has been hit hard.

From experiance of exactly the same damage on my Stealth ( ended up bouncing up the launching area with the rudder still down, since learnt to take the mainsail down before reaching the landing area with an on shore breeze ) it is a relatively easy repair. Not sure what age your boat is but forget the 4 hole pintles and replace like for like.

Simply be as accurate as you can and centre punch the screw and starting off with as small a drill as possible, drill a pilot hole. Drill progessively bigger until you start to get close to the edge of the screw ( you will almost certainly not be dead centre ), purchase an easy out ( basically a reverse thread tap on Ebay or likes ) and try to remove the bolt. The heat from the drilling is normally enough to free the thread. You may even find by drilling a bit sideways, as you will, the remaining bolt will break into pieces, a small screwdriver will remove the bits.

On my boat someone had drilled the thread out sufficiently sideways for the new bolt to not be strong enough on one of the bolts and that side constantly kept letting go. I ended up making a 6mm thread in the middle of a 10mm piece of stainless steel stud ( threaded part of a bolt ), drilling the hole oversize and epoxing in the new piece of stainless. Make sure you use the new Pintle as a guide though to get correct spacing of the holes. Seems to work well.

Be patient and work slowly and precisely and you won't have too many problems