Yeah, that's why I refrained from saying it was their oldest belief system. Those who have read the lore know that the dunmer were originally daedra worshipers. And yes, the Tribunal are broken, but again I think some might still hold on to the teachings. And Vivec is actually, from what I've read, not dead. He's.. Well gone. It's hard to explain, but the last we actually "see" of Vivec is in something called "The Trial of Vivec" on the Imperial Library site. I suppose a lot could have changed in 200 years, however, and he could be dead now. Also, after Sotha Sil and Almalexia were killed, everyone who you told that they were dead either thought you were a heretic or just insane, so maybe there are a few who believe they're still "around." The only problem I see with that disbelief continuing into "modern" day Tamriel is that they would have heard nothing from the Three for centuries, so a lot of people would probably start thinking that they really ARE gone. I don't know, this is just my two cents.
You're probably right. I doubt the old temple hierarchy holds much power any more, though. Probably there will be some sort of mysticism and legend involved with the remembrance of the old ways. Many of the oldest dunmer would still be alive, health permitting.
In any case I don't think we'll hear much about the dunmer ways, as it seems this is the time for the Nords to have their culture fleshed out, but I would still like to see some records of what has happened in the last 200 years of Dunmer history.