Jackson leaves Seattle with the respect of his soon-to-be-former teammates. He played through a torn pectoral muscle last season, never complaining about anything -- even as the Seahawks ran through receivers and shuffled their offensive line repeatedly.
Seattle's trade with Buffalo is not yet final. We should expect Jackson to rework his contract for the Bills. We should also expect the Seahawks to receive a late-round draft choice in return. A seventh-rounder that could upgrade based on playing time would represent fair value.
Jackson started 14 games and played in 15 for the Seahawks. He did what the team expected him to do upon signing from Minnesota in free agency: put his familiarity with the offensive system to use as a short-term bridge to whatever future awaited the Seahawks at quarterback. He was much better than Charlie Whitehurst, for sure.
Jackson struggled to make plays late in games (zero touchdowns, six interceptions and nine sacks in the final two minutes of halves). That was his failing in Seattle. But the Seahawks knew they were getting Jackson, not Joe Montana. And in fairness to Jackson, he wasn't exactly throwing to Jerry Rice or Steve Largent, either.
Jackson is ideally suited as a backup and would have fit as one in Seattle if the team hadn't been so aggressive about upgrading the position. That is one of the lessons of his departure after one season. Keeping Jackson would have been comfortable for the coaches. He knows the system. The Seahawks aren't into comfort. They're always looking for the next guy -- even the next backup.