I think as of now McGee will play around 10-15 minutes a game off the bench backing up Zeller. They will keep his job simply by keeping him around the hoop on both sides of the ball and not asking him to do too much.
I wouldn't be surprised if by the end of the season Olynyk and McGee are starters but they both will be coming off the bench and working their way into more minutes.
People that are acting like Olynyk isn't any good have a short memory. To start the season, he was very good shooting a high percentage, making the extra pass and rebounding. For a good portion of the season he lead our team in VORP, BPM, and Win shares. He might not have met your expectations but lineups with him in them did better than those without him.