They didn't earn Werner's death. In 10 seasons of this show they've always earned every single death, it was always completely believable that that person would kill in that exact moment. Even when the writers purposely shocked us by having Todd kill the kid, we found out over time that Todd was a sociopath who was capable of anything and had no moral limits underneath his friendly exterior.
But we already know how Mike is going to end up. And Mike isn't that kind of killer. EVERY person Mike ever kills is a killer himself, either the crooked cops who murked his son or various shooters for the drug cartels. That's it. He's not an executioner, if he was then at some point in Breaking Bad he would have offed Walter much, much earlier, cause Walter fukked up way more than Werner fukked up.
Here was a guy who avenged his son's death and was just trying to take care of his family. Would he have killed Werner, just a friendly overtalkative engineer who missed his wife, solely to protect Gus? I don't see it. If you say, "Gus would have killed him anyway", nah, Mike could have had Werner on a flight to Germany in no time and Gus don't have no reach in Germany. If you say, "But Gus would have killed Mike if he didn't do that"...based on what? Gus is a scary dude but he's also a careful dude, we haven't seen any evidence that he goes around hunting guys down just to kill them, nor have we seen any evidence that Gus got killers with better skills than Mike anyway. Gus is solely as southwest USA operation, Mike could have just put Werner on a plane, jumped his own ass back to the east coast somewhere (where his own contacts are almost certainly better than Gus's) and had his old dying body stay low for the few little years he had left. Would probably hook up with some crooked cops or another low-level crook and pulled small jobs while he sent money back to his daughter-in-law. Gus is too careful, since he knows Werner i gone and he knows Mike ain't gonna talk, he isn't gonna put his own neck out there doing something stupid solely because Mike ghosted on him.
The showrunners want us to believe Mike would just make an easy decision to off Werner in cold blood like there was no other choice. But we have like 6 seasons of Mike to know that he ain't like that, and there were other choices. An old dude like Mike ain't gonna kill a family man with his life still ahead of him like Werner unless Werner really deserved it, and Werner was clearly just fukking naive, he wasn't a bad guy. Werner died way to easy and they didn't earn it. I love these shows and this is literally the only plot point I've ever criticized them on.