[user104658]

Shane would have ended up making an amazing villain if they'd had him leave / be forced out instead of killed, then returning in a later season with his own group, maybe even as a Negan-style character (but more angry and less trollish). Although that said, they would have been taking a gamble as they wouldn't be able to hold the actor in a contract and would be relying on him being available to film, and he's done loads since TWD.

He was never really a full on villain at all... he did have an unhealthy connection with Lori and Carl (but for perfectly understandable reasons) but his main issue was that he saw Rick as weak and was scared that he would get them killed. It was supposed to be a major irony that after Shane's death, Rick actually came round to Shane's way of thinking pretty quickly... e.g. Rick was furious about Shane letting Carl practice using a handgun... then by the end of S3 Carl was toting an assault rifle with Rick's permission. And Rick has done a load of ruthless things in the name of keeping the group safe. The funny thing being, if Shane had seen Rick a couple of seasons later he probably wouldn't have had the same fears. He'd still have been jelly, but I don't think he would have wanted Rick gone.