You're worrying way too much. Cilic has only won ONE match against Fed, otherwise Fed has been owning Cilic, including a win at the USO in 2011. Cilic will not be in the zone like last time nor will Fed be as flat as he was that day.If he plays this well, no. Can't exploit his movement (he moves like he's 6ft2), no weaker side to attack, not enough firepower off the FH side to hit through him (Fed needs a very fast court these days for his FH to shine), not good enough defense/movement anymore to take the brunt of his attacks in BO5 and frustrate him into making errors. Marin also returns well and would be aggressive on Fed's 2nd serve, putting him under additional pressure.
I honestly don't think Fed would have a better chance against Cilic than Novak, would maybe even give him more chance against the latter actually.