It would depend on how big it gets.
For smaller mmos that are running off an engine that can’t be upgraded i’d want it to die off in 7-12 year mark. There would be limits to how versatile they can make the world and how many features/expansions they can make before it breaks.
For WoW they have been really good at keeping everything in working order. When I was in primary school / high school /uni absolutely zero interest in WoW. Saw it as a grind fest for people with no lives. Saw WoW players as the ultimate mouse pressing the ‘give me cheese rng button’.
It becoming easier in the starting levels and multiple ways of getting gear has made it much better for me.