It's not like Hooker has pace to lose. People talk like Cale Hooker is 35 and is about to drop off. He turns 30 next month, and probably has at the very least 3 years of decent football ahead of him. Hartley would be insane to be happy to be a depth/VFL player for us when there is jobs out there for him that's going to get him paid, and have security.
Even slow players lose pace in their 30s. Jobe was never quick but he was as slow as any footballer I've seen when he came back from suspension.
It is quite conceivable that Hooker could become too slow to hold down a key defensive post as soon as next season. Deep forward may become the only real position he can have.
We should do what we can to keep Hartley, who I believe is more effective than many realise, although obviously it would be understandable if he decided to go elsewhere. He'd be starting 22 for most AFL teams.