He will do 7-9. These films make way too much money not to. Maybe he will get better actors this time around. Maybe he will not write or direct them either. If he would just get a producer and story credit these films could be great.
His first had notables like Alec Guiness and Peter Cushing. David Prowse was not really a notable but I doubt that they hired him just to pantomime (he was surprised when his dialogue was overdubbed).
The actors off old are dying off. Christopher Lee is the only notable "new" cast member.
I could see him handing over the directorial reigns again. Sounds like any future films would be like these are largely be shot in a computer. I don't know of many directors who would want to sign on for that. Peter Jackson still likes some location shooting.