I am happy he left RB as it opened the door for Max but he must be thinking that if only he was patient for a few years he would most likely be fighting for the WDC title in 2017 with RB. He showed no loyalty and patience with the team. It was a case of Vettel not thinking in the long term and making his decision based on emotions.
Now Max is going to reap the benefits next year and be one of the favourites to win the WDC while poor Vettel struggles with a struggling Ferrari. I can't see him coming back to RB has that door is now shut since neither RB driver would be looking to leave the team for the next couple of years.