1300 bottle caps, +4 karma for finishing and an additional +1 for killing Decker, and 1400 XP.
It is advisable to take Kane out in the Maltese Falcon before taking on this mission, as he can make the close quarters combat extremely difficult and will very probably kill the player or his followers.
After killing Decker, some or all of the remaining guards may surrender. They can be found later in the Basement of the Falcon. If engaged in combat again they will most likely repeat "I surrender!" once again.
If the player talks to Beth after completing this mission and mention that they were the one who killed Decker, she will give them six stimpaks.