Navas will play RWB IMO.
I dont see Kelechi as solely a central striker either,he often comes deep and can play the 10 role.
A right sided forward is a necessity for me also,Nasri doesnt cut it.
I don't think Navas will play RWB at all, I'm not really sure why anyone does. When was the last time Pep played a winger at full back? Never. He doesn't even play with wing backs when he goes 3 at the back - he nearly always plays 3-3-3-1 with 3 central midfielders and wingers that are pushed so high up that no one would ever call them wingbacks.
Instead I think Pep knows that Navas is a great player to have in the squad, and that most of the reason his crossing is so maligned is because of Pellegrini's incompetent interpretation of wing play, getting the ball to Navas as slowly as possible and asking him to cross into a box with 8 defenders and 1, 5ft 8 striker.
Under a manager who will get the ball to his wingers quickly, and behind the opposition defence, Navas' crossing will magically go back to how it was for the first 10 years of his career.