I think you should get a refund on that feeder since they only sold you half of one. j/k Keep him and name him Lt. Dan (as in the legless Forest Gump Army Lt.) I mean hell, that's pretty impressive. Its not even a fair fight if you throw him into the tank. Besides, he's one serious survivor, probably has an immune system of iron and will just introduce some mega disease into your tank. I don't know.
Seriously, I vote for letting him live on. Every time you think your life is tough, go look at the goldfish and think it could be worse!