Sup lads, Chelsea fan here.
I think that at this point, its pretty clear that he wants to go, didnt Koeman said that you guys would allow the players that wanted out to leave?
I dont see how you guys have much leverage here, he has 2 years only on his current deal, thats pretty much the same situation that Alexis Sanchez is in, and Arsenal look to be in quite a dire situation with him, if you guys dont sell him now, you are looking at a potential big loss, as he will have only one year on his current deal, and i dont think Everton can afford that.
I think that we will eventually compromise( if we havent already) and he will go to Chelsea( not that i want him mind you, my preference would be for Costa staying, but his head is clearly not here anymore).
But anyway, im expecting that we will pay a really big fee for him, something like 80M probably