I don't think Crofts would win the ball in midfield like Kayal can. He would if back to his best - and that's not going to happen I fear - add more goals than Kayal but they aren't that similar in my opinion.
I wouldn't risk Crofts just yet.. I think Ince can step up to play the Kayal role. He has to. Anyway no two players are exactly the same so you automatically get a slight change in style of play.