Considering that it is a non-stressed area of the receiver. It could be properly tig welded and re-machined, but JB weld has been used to repair much more critical items. You would be surprised at how durable it can be when properly used, and if attention is paid to insuring a good adhesive bond.
Try using JB Weld with a couple of strategically placed small pins for reinforcement.... or... you could go so far as to glue the Trigger Guard in permanently to support the whole assembly. I don't see any real downside of that, and that method would be very strong...Hell...The Space Shuttle and the Stealth Fighter are glued together...be creative...there's not much to lose at this point!
BTW...for future reference, roll pins are designed to slip in with very, very light tapping with a very light hammer.
Good luck!