I've had the unpleasant situation of facing that decision. My son hooked a LM bass of about 14" in our local lake which requires releasing all bass under 15". This fish had a hook rip it's gills and was bleeding, obviously not going to survive, but back in the water it had to go.
Thankfully it doesn't happen often, and the fish will not be wasted. The turtles, crawfish, and other scavengers will feast on it.