Is anyone surprised that Hamas and Fatah are killing each other? Not me. And that tenuous cease-fire they've got going on is not going to last. Hamas and Fatah are fighting for control of the Palestinian Authority. It is a natural outgrowth of Hamas winning electorally.
Because, again, if the only tool you have is a hammer, everything looks like a nail. Hamas has expressed itself politically through violence for years. Now it has the chance to govern and it can't do it. Not without killing people. Its only political expression is violence and wild-eyed rhetoric. To be more balanced, Hamas also has many charities and feeds the poor, etc. But it is how you communicate and negotiate with your enemies that makes you a leader.
The worst possible denouement would be Israel's involvement in this fight. Let them kill each other or learn how to talk themselves. It is a struggle they are going to have to resolve.