In my opinion, Sal is the beneficiary of a very generous contract given to him "in gratitude" for helping bail out Lou and the organization from a very dicey situation when Kovalchuk's contract put them over the cap. He sat out an entire NHL season due to "concussion, " being placed on the LTIR, thus nullifying his cap hit and allowing the Devils to go over the cap.
IMO, Salvador probably could have played that season, but was kindly invited to "stay sick" because it would help out the Devils. MacLean's short tenure as coach, putting the team in a downward spiral before Christmas helped cement the decision for both Salvador and the Devils to shut it down for the season. He wouldn't have to worry about his head, have more time to rest, and the Devils wouldn't have to shuffle any more cards around to make room for Kovy's salary. Win-win for both parties.
In exchange for that "cooperative spirit" by Salvador, not to mention the solid playoff run in 2012, Lou rewarded Sal with a 3 year deal.
This is why he is still on the team and still captain IMO.
That's an interesting theory. I have no clue if it's accurate or not, but it makes for good reading, LOL!