Unfortunately Fleury can't be left unprotected because of his non-NMC NMC (Rutherford has to be kicking himself about the language in that deal, but how was he to know? Fleury doesn't have a full NMC, but a partial one that prevents him from being put on waivers...the NHL doesn't recognize partial NMCs, so in this case he's seen as having a full NMC, despite the fact that he could be traded to 17 different teams without his consent).
That said...yeah, I really don't expect Vegas to bend Rutherford over a barrel here if this is the route that the Penguins go down. They'll get a pretty piece, but it's not going to be a 1st rounder. Considering the trade board barely considers Murray as worth a 1st rounder in a vacuum, the Pens are still likely to have to leave Pouliot unprotected. It's not just a case of the Pens paying full market value just to keep Murray, it'll be Murray vs. Pouliot/Schultz/Bonino/whatever and a pick. You also have to recognize who is running the Las Vegas team right now...GMGM isn't the type of guy that burns bridges, and Rutherford is the type of GM who will make sure Vegas gets something decent for their side of the bargain (remember, for better or worse he made a fair market value deal to the Pens to get Jordan Staal back when he was with the Canes, despite Staal demanding a trade to Carolina...he'll make it worth Vegas's while to look somewhere else for goaltending, and there will still be plenty of quality options available). On a related note, Schultz is a RFA again after this season, so if he has a good year he'd also be a very appealing option for Vegas considering how much value puck-moving RHDs have in this league. It's hard to imagine either Pouliot or Schultz being protected over Letang, Määttä, or Dumoulin and you have to imagine young PMDs will be near the top of what GMGM is looking for.
We've seen these kinds of moves before, and I expect we'll see them again. I wouldn't be surprised in the least if the Pens roll into 2017-18 still with the tandem of Fleury & Murray...we'll just be short a good defenseman with a ton of upside and a 3rd round pick.