Not the end of the world. I get why people would be hesitant to bring back Colby. His 0.4 fWAR is pretty ugly and i can see why one would want to move on from that. I just see a player that was looking at a massive contract post 2013 and has a good chance at providing surplus value on a one year deal. (and then maybe a QO draft pick, or trade deadline talent). The low fWAR is pretty much due to his UZR and if we average his UZR from his last 3 years. ( about the time it takes to stabilize) i think it's fair to say he's not as bad defensively as the metrics point to this year. (Also, probably wasn't as good last year as the metrics indicate).
I just hate to see him walk for nothing.