I don't reckon so. I think Iniesta is the same player Xavi was three/four years ago. He'll slot into the Xavi role and then drop deeper as he gets older as Xavi himself has done. Personally I also think Busquets could push forward and do that role.
Also I think its a bit much ruling Thiago out already seeing as Xavi didn't hit his peak until his late 20's, hes got many years yet to develop into that player. But my bet is Iniesta into the Xavi role, Cesc into the Iniesta role. Then when Iniesta retires, Cesc into the Xavi role and Messi into the Iniesta role, with Deulofeu or Dongou taking the Messi role. etc..
And this will carry on until the oceans are dried up and the world becomes uninhabitable...
In theory, it seems so, and I have to admit, I thought this is what is going to happen too. But in reality, Barca have tried to play many games without Xavi, it just isn't the same without him. This is why even half-fit Xavi gets to play vs Milan, both legs, and PSG. He has been injured, been playing on injections. If it was as easy as you put it here, Barca would have played Cesc instead of him and that's that. But it is not so simple...
Talking about Xavi and Iniesta, I want to remind everybody about Cesc Fabregas. When he was at Arsenal, Cesc was frequently compared, sometimes favorably by certain people in the media and certainly Arsenal fans. Apparently, he makes more risky passes, has better long balls and more goals... whatever. But since he came to Barca, and has been playing on the same pitch with Xavi and Iniesta, we see a clear difference in levels. Between historical players that are Xavi and Iniesta, and good players like Cesc, Pirlo, Alonso and other contemporaries.