I'm thinking if we can trade him at the draft, we'll get the most back for him. The reason for this is that he will most likely be injured at some point in the season, so we'd probably only get a mediocre pick/prospect in return. If we move him at the draft, we may get a better pick/prospect in return.
I'm not exactly sure what to trade for him, but if we added him to a package of some sort, we might be able to get a decent 2nd line C and perhaps a decent 3rd/2nd pairing RD (to fill in for Stone and eventually to pair with Connauton). I'm not sure what else would be involved in the deal, but perhaps Perlini, Dahlbeck, or MacInnis (or picks) might be of interest to some teams (maybe Detroit)
I'm still not sure if the above will land us what we'd need, but if we keep Hanzal, my guess is the extension since he'll probably be injured around the trade deadline.