Why did Danny Archer stay back to recover the diamond in Blood Diamond? Was the diamond his only escape out of Africa? Or was he sympathetic towards Solomon and wanted to help him recover his family?
I watched this movie twice, and I think that Danny Archer is a pretty complex character. However, I think he is just selfish and wants the diamond for himself, and do not want to share with his former mentor, the Colonel Coetzee. He cares more about the diamond than Salomon and his son.
To support this theory, we just have to look at how he gives his mentor the way to make Salomon talk, his son. In fact, the only moment when he acts like an honorable person, is when he is forced to because he knows that he will die because of his wound. Every moment in the movie where he does something good is just in order to get closer to the diamond. Even when they are digging out the diamond, he attacks the mercenaries because he knows that they will kill him.
Danny Archer: Hey, boet, have you got a smoke?
Soldier: Smoking will kill you. Sorry.
Danny Archer: It's all right. Time I quit smoking anyway.
With this dialog, quite recurrent in the movie and the fact that the soldier points his gun to him, he knows. So I think that if Colonel Coetzee wouldn't have wanted to kill him, he would just keep his share of the diamond and respect the agreement with Colonel Coetzee.
So the first option is correct, he wanted the money of the diamond to leave Africa in my opinion.