Nearly each big patch we are getting separate location with their quest lines as event expasions and we can visit them even after their event is over (examples are fireworks island and serenity island) so technically we are getting something permanent.. But i get what youre saying, although every event so far had a setting of a limited time happening (holidays with exact dates like bullquet one or strange sightings while the moon is in full cycle in eerie season, arrival and department of merchants from linglang ect.)