In Killing them Softly at the end Brad Pitt says that Dillon died this morning:
Dillon's dead now fucking pay me.
How did Dillon die? Did we watch it happen or no? I never really saw Dillon much in the film.
Dillon has been unwell throughout the movie. Presumably in the hospital with a heart attack. We first learn this when Brad Pitt's character, Jackie, first arrives and is having the conversation in the car with the Driver character.
Driver: They told me when they heard that if Dillon wasn't available that I was supposed to talk to the fella that he sent. Is that you?
Jackie: I don't seen nobody else here. Do you?
Driver: So they were very concerned when I called Dillon, and Dillon said to see you. They are very concerned. How is the fella?
Jackie: Ah he's not good. He told me yesterday that it feels like somebody stuck a knife through his chest.
Driver: So he probably won't be able to handle anything for a while.
Jackie: He sure cant' right now. Personally I think the guy is in very bad shape.
At the end of the movie, after Frankie, Russell, and Trattman have been hit, Jackie meets the Driver again in a bar to collect his payment.
Jackie: There's only thirty in there....The price is fifteen.
Driver: Dillon charges ten. Recession prices. They told me to tell you that too.
Jackie: They made a deal with Mickey for fifteen.
Driver: ...you're filling in for Dillon and you get what Dillon gets, no more. You talk to Dillon; take it up with him.
Jackie: Dillon's dead. Dillon died this morning.
Driver: Ah, they're gonna be very sorry to hear that.
Jackie: Sure. Sure they are. Its gonna cost em more.
Whatever what causing him to be bed ridden this entire time has finally killed him.