Would be cool if the last boss was more dynamic like the events where you don’t really beat him but drive him and his minions back each time you “defeat” him and every now and then he gathers power to steamroll over players and villages to randomized points where you have to set up defenses with more events for a last stand kind of battle before it resets so players have to drive him back again.
THEN, just before a content/lore/expansion/whatever update there’s an epic instanced (so all players can experience it) last battle.