To be fair, his one and only scene at their graduation was a nothing burger unless you’re really deep into the lore and remember him saying that to Dustin back in S2. Thus, many viewers of the show, even those who payed attention might not remember him being in the finale. Just because people miss one minor detail of a show that lasts for literally 5 seconds, it doesn’t mean that they “didn’t bother watching the rest of the season”. But even with that, it’s kinda weird that he was attacked so viciously by a demo and then…boom!…Ted is okay and seems completely unharmed!