What if....

[Gene C]

It's not popular here, but I think Booth would have dropped the Deringer and quickly retrieved the revolver he had with him and made an even cleaner exit.

Since we're pretending, I'll pretend the revolver misfired too (like Payne's) , so he had to use his second deringer. That gives Rathbone a little more time to react, but he sustains a more serious knife injury. Without Rathbone clutching at him, Booth goes over the rail a bit smoother, but still injures his back when he lands on the stage. Same end result. (According to my time travel experience, you can't change history)