If there is one thing that the mainstream comic industry is obsessed with more than life itself, it is the status quo. That all important baseline story that characters may stray from occasionally, but will always inevitably return to regardless of how much it infuriates readers.
However, that doesn't mean that some things don't end up sticking for good. In fact, whether it's in standalone maxi-series event comics, or within the pages of a certain character's book, there are plenty of times that an event in that character's life permanently changed their place within their universe.
A lot of comic writers do this by just killing a character off, which CAN work under the right circumstances, but often times readers just see right through it as a ploy to ratchet up sales. There are multitudes of other ways to forever change a character's life for better or worse. From a permanent shift in their world view, to a changing of the guard causing them to reevaluate their alliances.
These single events, whether we like them or not, have rippled out through their respective character's lives and can still be felt to this day.