Alduin is unnecessary to reload the Mundus for an update, because Talos defragments it. Of course, the Thalmor are trying to uninstall him. If Alduin eats the world, time restarts at the Dawn Era anyways, so Alduin is advancing the Thalmor's goals. Talos needs to remain as to stop both Alduin and the Thalmor.
Hmm, the way I recall it Alduin doesn't delinearize time. He just winds it back to zero, and then lets it run linearly again until it runs out, and he eats the world and sets everything back to zero again.
Also, saying "time restarts at the Dawn Era" kinda doesn't make sense, since there really isn't a real notion of time as we know it until after the Dawn Era.