If it werent for the fact that he would play for the world junior + memorial if he stays in the ohl, i would rather have him in the nhl
Sorry if I sound rude, but that's flawed logic.
You either want him in the NHL because you think it's best for his development, or he goes back to juniors, regardless of the Memorial Cup and whatnot.
Whatever could happen in juniors is secondary to what he'd be learning in the NHL. The Memorial cup is like a 5-6 games tournament against kids. Sergachev would learn more just by playing 1 period against NHL opposition (if he's ready to do so).
In my opinion, Sergachev should stay if he's good enough to be our #6 dman. You don't want him to rot on the bench, but you do want to quickstart him. Because after the Subban/Weber swap, we're now working on a clock.