How Battlestar Galactica ends (theory) 

Galactica has one jump left before it becomes useless as a starship so they jump back to the home planet that was destroyed by the Cylons at the start of the show.

They arrive, and as predicted the ship is a mess.

They send a landing party down to the planet, but when they come back, they die within hours. Autopsies reveal that the planet no longer supports human life. Only one person from the landing party is unharmed, Kara "Starbuck" Thrace. Now they have to figure out why.

They study her blood and discover by accident that it is identical to the little girl who is half Cylon and half human, the one who saved the President's life with her blood. They send the President down to the planet and sure enough she survives. They send the little girl down and she survives too.

I forgot to mention that the planet kills pure-breed Cylons too.

So they now have a plan. Lots of cross-breeding between Cylons and humans forming a new hybrid race. Kara is the new leader, the prototype, the only adult among them who's healthy (the President is still dying and the kid is too young, everyone else who will survive hasn't even been born yet).

Fade out. Battlestar Galactica is over.

The End.