as much as iniesta is one of my favourite players, he is not as effective as pedro is in a wide forward position (though he can certainly 'do a job' there). Furthermore, guardiola brought pedro through the system and i can't imagine guardiola 'moving' pedro for really anyone. Pedro's age is also a plus compared to iniesta. This is different from the zlatan situation where there was a like for like swap in the system (eto'o out, zlatan in). The basic shape and tactics remained the same. Guardiola isn't like madrid, he wont feck up his whole philosophy to try to shoe horn fabregas by dropping either pedro or busquets permanently.
If fabregas moves to barca, he'll either have to wrestle a position off of iniesta or xavi, or sit on the bench. simples.