Theoretically, could a mod perma-ban all the other mods/admis, unban all the spammers and such, and have AG turn in to a flamming/trolling/spamming wasteland?
No, since mods are unable to permaban. Carlie could do that, she could demod them too. A mod in general are able to temporarily ban other mods, yes. So they could do that if they went crazy. If they keep up the ban, that is. I do predict that they would be stopped relatively fast if it happened, the moment the staff got to know about it.