Though I do know a lot about NPC extension, I'll admit I am no expert on NIC extension procedures. Still, I'd imagine the school has to approve the recolonization of Strong Southern Fraternity, and it would be up to those two parties to decide when the best time to return would be, and that may very well be AFTER you graduate.
Strong Southern Fraternity will be back at your SEC school at some point if they are as strong in the South as you say they are. They probably own their house. Point is, it's a matter of when, not if, and they don't need you to help them. The decision of when they return is not going to be up to you. Why would they even want a group of guys with no concept of loyalty recruiting members for them?
North-South differences aside, I'm sorry your chapter became something you don't like. I'm sorry you're in the minority. I'm sorry you've given up trying to improve your chapter. But most of all, I'm sorry that you don't give a shit about your alumni membership to the point where you'd throw it away to be able to say that you "helped" a strong, presitigious organization that doesn't need your help in the first place.
Your fraternity is so much bigger than your chapter. You might find that you connect with members from other chapters (from the South, of course

) when you are an alumnus. College is 4 (or maybe 5 or 6) years, and your alumni membership is for the rest of your life. If you keep your membership, you can help your own chapter recolonize once the ding-dongs manage to get themselves kicked off as well.
ETA: Out of 80 members, 15-20 who give a shit about the chapter and work to enact change ARE enough.