I seriously doubt they had no real plan for end game in Vanilla considering Tigole aka Jeff Kaplan as well as his Legacy of Steel guildmate Rob Pardo were huge raiders in EverQuest before coming over to make WoW. They also had Alex Afrasiabi, AKA Furor, who was the imfamous guild leader of Fires of Heaven. So for 3 super hardcore raiders to be running things I doubt there was no concept of end game for Vanilla.
There were AoE stomping infernals that would teleport out of bounds players to GM Island and destroy their hearthstone. GMs would log in, see them, give them a verbal tongue lashing and then teleport them back to civilization.