You can make all raids. At least 2-3 years. You can do this on the other side. Another 2-3 years. You can perform all the classes, and then put all the classes in BIS gear. Multiply those two years by eight, or sixteen years. You can speed up the game (the game itself can last a lifetime). You can use PVP. ()
Why do you care if it’s “out of date”? Why do you want to play “forever”? In particular, why do you worry about whether Blizzard is “financially infeasible”? Are you a blizzard accountant?
Just play it until you’re no longer interested. Then stop playing. It’s very simple.