I guess it depends on if they think he can overcome the injury in the short term or the long term. They certainly persisted with Menzel through 4 knee reco's and kept him on the list. I don't think Geelong would discard Gregson callously, they're not that sort of club. We'll have to wait and see how it unfolds in a few months.
If the experiences of Cowan, Menzel, and McCarthy are anything to go by he's got at least another 3 years up his sleeve yet.