Dumb post, Valverde won't be sacked not matter how badly he does in the CL as long as he wins the league. It doesn't matter what you, I, or any other fan wants; as long as Valverde wins at least one of the CL or Liga every year he will not be sacked and that is a FACT.
As for Dembele, next season will be the one he breaks out in. He will be a bit older and more mature at 21, have lived in Spain for a year, would know the language and his teammates a bit and would have had some time following a stricter diet with better treatment and exercise plans to help maintain fitness and avoid injury.
Not to mention most of the trash like Gomes and Vidal will be cleared by then along with Paulinho moving to the bench, which should open up a clear spot for him. I also don't think Valverde sticks with the 4-4-2 beyond this season as it was never his original intention, but injuries and unseen circumstances forced him into playing it and it's too late to change it at this point in this campaign. With the players we have right now the 4-3-3 is the clear choice and expect to see that starting next season.