The right thing would be to convince Assad to offer a truce, step down, and allow a democratic election to happen. He'd have to be given protection, too, otherwise he'd never agree to stop, because he'd fear too much for his life.
Of course, even if they do convince Assad of that, it doesn't mean things will go smoothly. The "rebels" might still be upset if they lose the election, which is why it's so important UN or whoever needs to guarantee fair elections. It's the least they can do to appease the rebels, so they don't want to start the civil war all over again. They could even guarantee some sort of remuneration from the state for all the people who lost a family member in the war.
This is the least violent, and best solution for everyone involved.
Of course, even if they do convince Assad of that, it doesn't mean things will go smoothly. The "rebels" might still be upset if they lose the election, which is why it's so important UN or whoever needs to guarantee fair elections. It's the least they can do to appease the rebels, so they don't want to start the civil war all over again. They could even guarantee some sort of remuneration from the state for all the people who lost a family member in the war.
This is the least violent, and best solution for everyone involved.