Somewhere out there there's a bullet with Frank Castle's name on it, and let's face it, it's probably in the barrel of his own gun.
The Punisher Kills The Marvel Universe isn't the only one of his stories to end in suicide. In a 1998 comic, he put an end to his tragic tale of loss and revenge by putting a bullet in his own head in a dark alleyway. The alley ends up becoming a shrine to Castle and his vigilantism.
There's a certain inevitability about Punisher's story ultimately concluding this way. His war against the mob is basically a suicide run, anyone he cares about is long since dead, and he's too skilled to be killed or caught by the authorities.
In typical Marvel fashion, the comic book giant decided death shouldn't be the end for Punisher and had him transformed into a supernatural killing machine, but that's a whole other (bonkers) story that's since been retconned.