I've repaired a few right and left feeds that came out due to abuse. It's hard to get them out without scratching them up, though.
I'd probably try to make a threaded plug that goes into the neck, and a clamp on the outside.
On re-attaching them, I'd scratch up the area of the feedneck that was covered by the receiver, degrease with brakekleen, and glue it in with good quality epoxy- In this case i used Brownells AcraGlass. JB Weld would do a great job too.
I would carefully run my pinkie inside the receiver via the feedneck to see if I could feel any sharp edges. Sighting through the rear of the receiver should confirm that the neck is 100% lined up.