Theoria

How it must end:

(1) As Adama’s volunteer force attacks the Cylon colony ship, the fleet renews civil war, this time attempting to seize control of the basestar. Both battles are catastrophic and everyone dies down to the last person, human and Cylon alike;
(2) Cylons or humans from a previous cycle of history miraculously and mysteriously appear amidst the battle between Galactica and the Cylon colony ship, fighting stops, but only momentarily, and then resumes with everyone dying (c.f., end of “Children of Men”), possibly with the mysterious fleet killing everyone.

But, this is how it will end:

(3) Happily ever after. Hera will be rescued, human and Cylon will agree to disagree and once again go their separate ways. Galactica will be mortally wounded in the battle and Tigh and Adama will elect to go down with the ship. Everyone else escapes.