Just to clarify, for reasons I am not going into Koeman is the most likely replacement. Jose is not out of the frame, but as a club we cannot put all our "eggs" in the "Jose basket" for obvious reasons.
Armed with a serious amount of cash, and given the task of rebuilding - let's be realistic, that's the task any incoming manager faces, the Martinez project is dead and we're likely to lose at least one of our "star" players in Lukaku, perhaps Stones as well - albeit receiving significant fees for both, Koeman is a pretty decent choice, and one who has the potential if not yet, the proven ability to become a winner.
I'm pretty certain that a revamped Everton squad, under Koeman would have be highly competitive in this year's PL, so why not in next year also?
There's also the very real prospect of a Director of Football being appointed, integrating all of the junior levels with the senior side - an extremely valuable asset if this proves to be the case.