The question was whether there's a naturalistic explanation of unity in the universe. If we're positing a multiverse, we've lost that unity at the outset. Our universe might be unified, but only in a relative sense. Relative to our limited perspective of the whole, there would a "single natural order," but in reality there would be everything under infinite alien suns, the exact opposite of a single system. Then the question would be whether there's a naturalistic explanation of the meta-system, of how universes emerge from the deeper conditions of a multiverse.

Or again, if you're assuming a cycle of universal growth and decay, we'd lack unity unless this were Nietzsche's eternal return of the same.