Well if it was me I would retire. He has made his mark, and changed film making for the better. And he's in his 50's now. If he started Ep. 7,8,9. He would be in his mid 60's. If it was me I would retire to spend time with my family. He has made his mark and money. I would regret not seeing the saga come to a real close, but I would understand him retiring.
P.S. Even if he does retire, his children and friends can take over.
Maybe their will be Ep. 7,8,9. No telling where Star Wars will go.