I believe that generally they come in the form of a "player option". If Grebenken wants (is willing) to ride the bus in the AHL for $70k -- then of course he can do that.
I suspect it'll probably come down to convincing him of the advantages of remaining with the Marlies (same city, same practice facility, easy callup) as it goes towards a future NHL career; whereas if he goes back to Russia, he's basically going to be stuck there for the year.
From a hockey-sense, he's better off with the Marlies.... but he's only 20 years old, he hasn't exactly secured himself a comfortable bag of cash. Turning down a couple million probably to play in the KHL; in order to chase an NHL dream, is a little bit of a tough proposition.
Maybe it's a situation where barring a completely lights out performance, he's going back to the KHL, with the mindset of joining the Leafs/Marlies upon the KHL season's completion.