Even setting aside the Marner talk for a second, the Penguins are in a position in the next couple of years where they'll likely have to be handing out significant contracts in UFA, just because they won't have any more highly paid players. Even next year, they're sitting at $65 million without making and moves and $15 million under the cap floor. With cheap guys like McGroarty and Koivunen looking to play notable roles next year and veterans that will be moved, they may have to hand out big bucks in open positions.
I think the idea I like the most is splurging on defense, specifically giving Fabbro and Chychrun long-term deals. The Penguins D prospect pool is pretty limited beyond Brunicke, Pickering and Pieniniemi, and you'll need guys capable of eating minutes to insulate the young guys. Fabbro and Chychrun are both barely UFA ages, where they'll only be 27 when they're signing their deals. I'd easily give Chychrun like a 6x7 deal and Fabbro a 6x4 deal and just keep that as a pair for as long as I can. I'd personally trade Karlsson for futures and go with:
Pickering-Letang
Chychrun-Fabbro
Graves-POJ
Eventually Brunicke comes up and replaces Letang once he retires.