Sam Gagner is one of sixteen players who has filed for salary arbitration. Not many of these cases actually end up before an arbitrator (one of the sixteen players, David Perron, has already signed), and I don't expect Gagner to get there either. In fact, I think a trade is more likely, much like we saw with Andrew Cogliano in a similar situation last season. The two parties weren't close to a deal, so the Oilers sent Cogliano to a team willing to (over)pay him. Is that Gagner's future too? I'm not sure, but to me, the decision to file at all doesn't seem very astute.
When I looked at players of similar age with comparable platform seasons during this CBA, it didn't look like the arbitration process would be a sure way for Gagner to get a big raise. Of course, Gagner and his agent may have other players in mind that they're hoping to use, but at the very least, they know that the Oilers can make a pretty strong case to keep Gagner's salary in the $2.5M to $3M range in front of an arbitrator.
It seems to me that Gagner's better bet would have been to try to find a team willing to sign him to a lucrative offer sheet. Darcy Regier, for example, might relish the idea of signing a young Oiler forward to an offer sheet after the Oilers pushed the price up on him with their offer for Tomas Vanek a few years back. The Sabres just traded Derek Roy to Dallas, so there's room for Gagner at center, and the club has plenty of space under the salary cap. They could offer between $3.5M and $5M per season and only need to give up a first and third round pick.
It's possible that Gagner explored that option and found that no one was willing to pay up. I'd actually be pretty surprised at that, but it is possible. It's also possible that Gagner simply likes Edmonton and wants to continue playing there. That would be great news for the Oilers because it will help them to get a better deal. If that's the case, I would humbly suggest that Gagner take a little bit less money and insist on a no-trade clause in his next contract to avoid being Setoguchi-ed. If he takes a discount and becomes an attractive trade option, I could definitely see it happening.