SPOILERS! After Sunday night’s episode of Fear TWD where we lost one of the original cast members since the first episode, Nick Clark, many people were saying “how could they kill Nick off the show?”, “how dare Gimple kill more people off?” – well it wasn’t the showrunners or Scott Gimple’s fault, the actor, Frank Dillane, wanted out of the show since season 3. This isn’t really surprising as if you saw Frank Dillane during interviews or at Comic Con, he looked as if he didn’t want to be there.

Showrunners Andrew Chambliss and Ian Goldberg answered questions about this big character death in various media outlets, but here’s quotes from both of them, telling everyone that it was Frank’s decision, not their decision to kill his character off the show.

Ian Goldberg: Well, one of the hardest things for Andrew and me, when we came on as showrunners, is that Frank had asked, even prior to us coming on to lead the show, to pursue other opportunities. So it was really, for us, crafting an emotional exit for an incredible character that he played. That was something that was just really important to us, was how to tell an emotional story for Nick and to send off his character in a fitting way. But with the way that we are playing with time in these first eight episodes, we will be seeing Nick again, as we do have multiple timelines.
Source: ew.com

Andrew Chambliss: It actually goes back to season three, before Ian and I even came aboard. Frank Dillane had asked the producers and AMC if he could leave the show, because he wanted to pursue other opportunities. One of the first things we were tasked with when we came on to run season four was to really find a story that would give Nick a fitting sendoff. He’s been with the show from day one, so it was very important to us and to Frank to find a death for him that was emotional and one that would ripple forward throughout the storytelling.
Source: hollywoodreporter.com

Update to post: added the below quote from actor Frank Dillane, where he was asked what led to his decision to leave the show.

Frank Dillane: I had been doing it for three or four years, the show has undergone many changes in terms of different people in charge, all of this stuff, and I just felt like the beginning of this season kind of felt like the end of an era with this show. And television is hard work, and you have to shoot a lot. I also missed Europe very much. I’m not American, so after a while I get quite homesick and all of those things. I also felt like we had achieved what needed to be achieved in the first few seasons, so I thought it was time to keep moving.
Source: yahoo.com