That doesn't mean Clifton's departure is a major loss for the Packers. (Nor was it a surprise.) Green Bay already has essentially gone through a season without Clifton; it was the best team in the regular season last year without him.
Marshall Newhouse isn't anyone's idea of a Pro Bowl tackle, but he was capable last season. We'd argue he was around league average without a lot of experience, so that should mean he has room to grow. The Packers also drafted Derrek Sherrod in the first round last year. While Sherrod didn't show a ton as a rookie, the Packers are one of the best teams in developing talent.