Oh god mate, the most liley scenario is what
@GrandOldTeam said a bit earlier about Riaola having a deal lined up at a certain price already, and that's why he wants that specific value of release clause inserted.
But if the club don't back down on that then he's faced with either losing a lot of money or cutting his losses and trying to get the best deal/profit he can do for his client (and thus himself)
Money etc may not be the driving force for Lukaku (although turning down an extra 70-90k per week is stretching how much it doesn't matter to him I'd guess), but one thing without any doubt is that the money is all that matters to his agent.
If i was a betting man, I actually think he will sign a new contract - with the release clause that he wants, but with it not being activated until summer 2018 and maybe a few extra quid thrown into the contract (or it being backdated etc) as an extra sweetener.