The rules are clear on Manifested Ephemerals (CoD, p. 129):
Physical attacks on a Manifested entity that would normally cause lethal damage only cause bashing damage unless the attack utilizes the entity’s bane. Despite appearing to the naked eye and being solid, a Manifested spirit, ghost, or angel doesn’t have any internal organs to injure...
Ephemeral entities that lose all Corpus from lethal or aggravated wounds explode into a burst of ephemera, stylized to their nature.... The entity isn’t actually dead, though, unless it has also run out of Essence. If it has even a single Essence point remaining, it reforms, hibernating, in a safe place (a Conditioned location, usually).
However, do the same rules apply to angels in Cover? Does an angel who receives only Lethal damage equal to its Corpus survive in Twilight to perhaps return one day to avenge themselves?