Without any additional moves, I think this team is probably sitting with this base for next year:
Rakell-Crosby-Rust
Bunting-Malkin-XXXX
Heinen-Glass-Tomasino
Lizotte-Ponomarev-Acciari
Hayes
XXXXX-Karlsson
POJ-Letang
Kolya-Desharnais
Graves
Nedjelkovic-Blomqvist
I think the only young guy "guaranteed" a spot for next year is Ponomarev, and that's largely driven by him becoming waiver eligible. I think McGroarty, Koivunen and Pickering all more likely start in WBS without a great camp.
With this, they'd need a top-6 winger who can kill penalties and a top-4 LD. The PKing thing matters because they only have 5 established PKing forwards between Glass, Rust, Lizotte, Acciari and Ponomarev, and Sullivan has been pretty consistent about wanting 6 PKing forwards in his lineup. I'm not saying "bring him in because of this" obviously but Marner would actually add a 6th PKing forward as well.
Personally I'd offer a dump truck of a deal to Marner and a short term and high AAV deal to Orlov. Use any remaining cap space to bring in short term cap dumps for picks.