I’m pretty sure the last expansion will be Return of the Lich King. The game would come full circle and end on a high note. I’d be ready to set down my weapon and move on after that.
My dream would be for the lich to win and destroy the majority of the world setting up a WoW 2 in the future as the last survivors. Or just have us lose in the end and have it be game over. WoW should end in tragedy to teach us the sins of our bellicose ways.