Basically, everyone will die. They destroy the evil Cylons but the black hole sucks them in and the screen fades to black as we follow them into the depths of the gravity well.
Science fiction geeks the world over will riot at the Sopranos-esque ending. Kara Thrace will literally be the harbinger of doom, as the first ever TV show riots break out.
That is how Battlestar Galactica will end.