I can guarantee we wouldn't get equal value for Kessel in a trade. We would end up with one or more lesser players. Probably a 60 point centerman.
If he's not going to sign here, we have to trade him. And we wouldn't trade him for a proven ~60 point C. We'd have to roll the dice on a top prospect + lesser roster player.
Anyways, one thing to point out is that IF we have to trade Kessel, I don't think it means a full rebuild.
Blueline- pretty set longterm. Phaneuf+Rielly+Gardiner+Gunnarson+ Percy/Finn/Blacker/Holzer/etc
Wingers - Set longterm, unless both Kessel/Lupul leave. But presumably we'd be trading them for some good assets. Winger is the least important position on the team. Ideally Kessel/Lupul would be traded to help beef up the G/C positions
Centre - Pretty thing. Hopefully it can either get filled via our 1st round pick this upcoming draft, Mackinnon, Monahan, or somebody else (Barkov?), or via a Kessel trade, or via free agency with Getzlaf. All of them are longshots obviously, but say we did trade Kessel for a package that included a really solid C prospect, presumably without Kessel and with our goaltending we'd bottom out this year, and would get one of the top 2-3 centres in the draft. Which would give us 2 solid centre prospects, hopefully 1 of which becomes the player we need
Goaltending - Obviously a problem. Backstrom could be a shortterm answer in free agency. Otherwise you'd have to hope we got a good goalie prospect back in one of the packages for Kessel or Lupul.
Anyways, I'm not saying we SHOULD trade Kessel. Just that we absolutely can't let him (or Lupul, MacArthur, Bozak, etc) walk for nothing. And if we have to trade him, it's not the end of the world. Our blueline looks decent longterm, we should have a high pick this upcoming draft, and we'd presumably get pretty solid packages for Kessel/Lupul, though obviously not as good as what we ultimately gave up in the original Kessel deal.