I've seen Deus Esca blast four moon-shattering shots into it over the span of six hours or so, and every time it seems none the worse for wear afterwards.
It's kinda funny to me how after the story events they made a reason for the boss to canonically keep coming back, but every time he does he blows a large chunk of the moon to bits. There's only so much moon to go around, at this rate it's gonna be made of gravel within the week.