It will be around for a long time. Blizzard guys are very smart, and they actually listen to the community. With redesigning leveling they will reduce the grind making it more attractive for new players, and also easier for existing players to level up alts. They are implementing Ray Tracing which means a massive rework of old areas is to be expected. They also have all the money in the world so anything is possible.
I expect to see WoW exist for at least 5 years, probably a lot more. It is not unlikely that our grandchildren will play WoW.