Well, it's not completely dead yet.
That said, the combination of insularity, banhappiness, and insularity makes it impressive that it got as large as it did. I suppose in one sense, if you make a community exclusive, it adds cachet to being a member in good standing, but it was basically all about cyberbullying, down to doxxing, offline harassment, and publicly shaming people. "Making fun of stupid people" in the title header of the forum says all it needs to. The poster in that questionablequesting thread who called his custom title a "dunce cap" gave a perfect example of bullying by public shaming.
I think it was starting to shrink even before Wong left. The more litmus tests you add with "agree or you're banned / bullied," the more people leave over time.
On that subject, searching for information on what Curtis Saxton is up to these days after he came up in the other thread and on the subject of SDN's love for public shaming, apparently Saxton is now being quoted as saying "DO YOU WORSHIP HOMOSEXUALS?" in the sig of one of the remaining active SDN members, linking to a source that's over in a non-public forum section.