I seriously doubt they will return to San Fran when the tour arrives there. They will most likely still be performing on Broadway. if not, probably looking for new roles. It's kind of like when the Cleveland Browns left Cleveland for Baltimore, and then Cleveland got a new Browns team. The new team had the same name and colors, but the team they knew as the Browns before is now in Baltimore. You know what I mean?
They are now casting for the U.S. tour, which will begin next spring. I would keep checking this site for updated information:
http://www.musicalschwartz.com/wicked-tour.htm
Mark