If they don't pay him out then they're effectively finished here.
They have a choice - pay him the 84 bitcoin & continue running a trusted site & make profits for an unlimited time
Or
Scam him & pretty much end their business with a destroyed reputation over 84 bitcoin.
For the above reason I'm confident they'll pay him out.
Maybe there's a third option: come up with a semi-convincing story about how OP cheated.
He played "live roulette", which generally means FJ paid some third-party company to spin a roulette wheel and broadcast video of it happening, while FJ took bets on the outcome. I don't know what assurance FJ have that the company spinning the wheel is broadcasting it live rather than with a 60 second delay. Such a delay would give them plenty of time to place bets on the number that already came up.
I guess this kind of cheating is what they are worried about, but I've no idea how you would go about proving or disproving it. I expect you just have to trust the third-party video feed provider that they won't play against you, felay the feed, use an unbalanced wheel, etc. Provable fairness cuts both ways.