I have a theory on why I believe Chuck will finally meet his demise at the end of Season 3:
The season finale's name is Lantern. Back in Season 1, when Chuck visited the hospital for the first time, the nurse said when trying to convince Jimmy to commit his brother: "Coleman lantern indoors? A camp stove? He could burn his house down." Jimmy had two perfect opportunities to commit Chuck to a mental institution and get him psychological help for his condition. In Season 1, Jimmy chose not to commit him, which was when he and Chuck were on good terms. In Season 2, Jimmy and Chuck were at odds with each other, but Jimmy still greatly cared for him, so he chose against it once again. It's easy to say that in Season 3, Jimmy and Chuck's relationship is irrepairable. Chuck's condition and his way of living with camp stoves and lanterns could ultimately get him killed.
Before Jimmy was arrested, the conversation he had with Chuck, where basically tells him that next time he is sick, he will not be there to help him is also very interesting. From what Jimmy said, it's clear that he no longer cares for Chuck anymore after all the trauma that's happened between the two brothers.
I also noticed in Season 3 Episode 4 when Mike is repairing Chuck's door, that the camera zoomed in on a propane tank in Chuck's house. Knowing Vince Gilligan from watching all 5 seasons of Breaking Bad and the past 3 seasons of Better Call Saul is that he is always very careful and puts these camera angles in there to foreshadow certain events in the future. The lantern and the propane tank would not go well together and I think this could very well lead to Chuck dying, which would be the last straw for Jimmy McGill and to finally give us Saul Goodman.
Overall, I stand by this theory of mine. I think it makes alot of sense and we will have to see what happens. But I think if Jimmy is going to become Saul, I can see Chuck's death being the cause of that. If this is the case, Michael McKean will definitely be missed on the show. While we all hate Chuck, he definitely brought life to him and there would definitely be a void left on the show without him there.