After 2 years, the servers will have to restart. Not only to allow the guys in Naxxramas to experience it once again, but also to allow new players to experience it from launch. Starting TBC in patch 2.0 was fun, which i did as i started playing in late classic. But starting in patch 2.4 or even 2.3 was not so much fun.
If TBC becomes a thing again. They should advance the classic wow servers and create new ones, or create TBC servers and reset the classic servers.