This is how it would go:

Bane and Skywalker meet on a scorched battlefield, the corpses of fallen Sith and Jedi alike littering the horizon. Bane recognizes Skywalker's immense power in the Force and does not underestimate him, but mocks the Jedi's adherence to the lightside. Luke coolly dismisses the Sith Lords use of dun moch as he has dealt with Sith Lords before and has touched the darkside himself. However, Luke realizes the Bane reeks of the darkside and is more powerful than any modern day Sith he has encountered. Luke offers the Sith one chance to turn away from the darkside, but does not invest much hope in such a thing happening.

The battle is fierce, their lightsaber blades not much more than blurs of green and red. The clash is ferocious as Bane unleashes dark powers Luke could only dream of. The Grand Master stands his own though, as he has faced down foes that Darth Bane would have never conceived would have existed in his time. The Sith Lord drinks up Luke's pain and anguish from the battle, but cannot consume his enemy's fear or doubt as Skywalker displays none of this. Bane is slighty perturbed that such a Jedi even exists to face him.

The battle rages. Bane is powerful, both physically and in the Force. Luke is losing the edge but he does not falter in his duty. Bane scores a blow and Luke falls to his knees. Bane lifts his saber in preparation of the death blow. The Sith Lord expects a rush of fear and anger to explode forth from his fallen opponent, however he only senses Skywalker's peace and focus in the Force. Bane is disappointed that he will not receive total satisfaction for the kill. In a moment of hesitation, Bane realizes he has made a fatal mistake. Skywalker was not focusing and preparing for his trip to the netherworld. He was planning his next move, calling forth his fallen lightsaber, springing from his feet, and in a blur too fast to imagine, up and over the Sith Lord to bury his saber deep into Bane's back and out through his chest.

The Sith Lord makes no sound and he crumples forward, only a slight grin on his face knowing he has been slain so beautifully by the most powerful warrior in the history of the galaxy. At the last moment, he remembers his real name: Dessel. He tries to cry out in penance, but it is too late.

Luke clutches his wound, nearly fatal. But he would heal, like he always did and will continue to face the evils that threaten the galaxy.