The Borg vs Superman
When Superman returns to Earth, in Superman Returns, the Borg had invaded and assimilated everyone on the planet. Due to the assimilation of Lex Luthor and the Fortress of Solitude, the Borg have understanding of Superman and Kryptonian tech.
How would Superman deal with this problem? He has no knowledge of the Borg, nor does he know how to reverse the assimilation process to restore humanity.
Does he destroy Earth?
Does the Borg assimilate him?
Would Superman leave Earth and try to find a civilization that knows the Borg and how to fight them without destroying humanity?