AMC
One of the possible endings had Walt, Jesse, and every major character dying in a "bloodbath."
In an interview with EW, Vince Gilligan revealed that there was "30 or 40 different permutations of the ending" for the series finale, "Felina." Mostly because they boxed themselves into a corner introducing Walt's M60 in the first episode.
"Out of cockiness or stupidity, 16 episodes from the end, we had Walter White show up in a beard, long hair, and a new set of glasses, buying an M60 machine gun in a Denny's parking lot," Gilligan said. "We didn't really know how we were going to get to that story point - we didn't even know what that meant or what Walt was going to use that machine gun for."
Trying to figure out what Walt would do with the giant M60 led Gilligan and the writers to craft an ending where having the gun made sense.
One of those endings had Walt shooting up a jail to rescue Jesse, which was ultimately scratched because the creators felt that Walt wasn't bad enough by that point to shoot up a bunch of innocent people. Another had him shoot up a prison bus in the same fashion.
Gilligan even considered an ending of killing off all the major characters in a violent wild west type bloodbath.
"At one point, we talked about killing off every major character," he said. "One particularly dark week along the way we talked about killing everybody - having some sort of 'Wild Bunch' bloodbath of an ending."
However, the conclusion they came to for the finale was ultimately the most "organic."
"The best way to go about this job... is to tell the story as organically as possible and to tell it brick by brick," Gilligan said. "You keep reminding yourself: Sometimes micro is more important than macro."