@OT
Re-allying with a stabber in the same game is an interesting topic, and my answer to your question would be, "it depends." First of all, you can't very well trust them. So whatever they say to you has to be cast in a shade of doubt. After all, they betrayed someone else, or maybe they betrayed you. In practice, the onus would be on the stabber to regain lost trust and demonstrate good faith. Second, the politics and positioning in the game may well require at least talking with the stabber. You can offer a truce and draw lines in order to make gains elsewhere. Better yet, they may need your help, and you can use the betrayal as leverage for a better deal. Third, you never know the circumstances that prompted the stabbing to begin with. They may have been presented with an offer they couldn't refuse.
In short, I would say that re-allying with a stabber in the same game is tricky, but always worth consideration. Best to keep them outside of kicking distance, all the same.