If Marin leaves, Isco signing would be good. KDB will not play in the attacking three IMO. He's being streamlined to play as the distributor in the pivot - so no problem there. Basically we'd have Isco, Mata, Hazard, Oscar, Moses for the attacking three with KDB as back up as he is able to play there and for the pivot we'd have something like Mikel, KDB, Lampard (hopefully), Ramires with Luiz and Oscar also being able to play there. That's the way I'd manage the team anyway.