While he may have once broken Batman and more recently wrestled Gotham itself from the Dark Knight's control, Bane could do away with his longtime adversary for good with a little assistance from the underworld. It's no secret that of all of Batman's villains, Bane is one of the few to successfully bring Bruce's world crashing down around him (even Joker admits he could have been the hero's greatest enemy.) But even with his long-game planning and Venom-enhanced physique, he just can't seem to put the Bat down permanently.
Bane's inability to thwart Batman has hung over him for years. Even when he joined the Secret Six, he was constantly reminded of his failure, bitterly laughing off anyone that challenged him, reminding them of how weak a challenge they would make compared to the Dark Knight. Bane achieved the closest thing to peace that a killer like him could with the Six, but still spent his time with the team obsessing over Batman and his personal legacy.
In Secret Six #33 by Gail Simone and Jim Calafiore, Bane gets the wake-up call of a lifetime when he and his ragtag group of mercenaries take the plunge into literal Hell. After an enigmatic "Get Out of Hell Free" card causes a schism in the group, the Secret Six find themselves among the lakes of fire, where their teammate Ragdoll has been newly crowned royalty among the damned. Ragdoll and his demonic coterie inform the Six that their sins mean they'll be confined to Hell as victims on death. As an alternative, Ragdoll offers them a place in his court of the damned, complete with dark upgrades that will assist them in torturing souls for all eternity.
The Secret Six all get new elements to aid their potential tormenting. King Shark gets an impressive suit of armor and a deadly-looking trident. Deadshot becomes a gun-infused cyborg. And for Bane, his strength and body are modified to a horrific degree, looking like a demonic version of Doomsday, the monstrous villain who killed Superman. After a moment of contemplation, the gang violently refuse Ragdoll's offer. Bane gets a brief moment to see how powerful he could truly be and easily tears down demon after demon, no Venom needed. Had Batman been anywhere in his line of sight, Bane would have done a lot more than broken Bruce's back. But Bane is a man with a code, and while he may one day be condemned to Hell, he has no interest in taking down his archenemy due to an unfair advantage.
Secret Six made a study of how truly terrible people justify their actions and form bonds, with the core idea that what makes the team hate superheroes is how they use superior power to set the rules everyone else must obey. Thankfully for the damned, that single principle meant the team felt unable to join their ally Ragdoll as rulers in Hell, instead taking on an army of demons to win their freedom and reject the offer of untold power.
Bane has challenged Batman in ways other villains can't, by testing Bruce physically and mentally, and has even won a few major victories. But despite his intellect and the added strength of Venom, Batman is just as skilled as Bane in mind and body. Bane's code is the one thing that made him think he didn't belong in Hell, but it just may be the one thing holding him back from truly winning. By choosing freedom and honor, Bane lost out on an enhancement that could have done away with Batman for good.