What happens if the bitcoin network becomes split for a long time?

[NeedsBitcoin]

Lets say that another cold war breaks out and cyber attacks divide the Internet, Or a space colony on mars when it is on the other side of the moon causes the internet to be split. At some points the internet is restored, does the bitcoin network merge the forked block chains?

What happens if someone gained access to both internets and double spent, and a lot of transactions occurred from the double spent bitcoins, how would it merge something like that? Would all 'tainted' transactions be reversed?