I'm pretty confident this is never going to happen with any coach unless Dybala becomes willing to sacrifice and play behind strikers, come back for the ball, contribute defensively etc.
I doubt even Pep would combine them in some kind of total football arrangement.
They both occupy similar spaces, like the ball, neither is a natural striker so they can't play alone as two strikers, neither contributes defensively and with pressing that much, neither is a winger... They're just too similar and either too good (Ronaldo) or unwilling (Dybala) to sacrifice for the overall defensive stability of the team.
Best case scenario is Dybala from the start of 17/18 season behind Ronaldo and a workhorse CF like Mario, Cavani, Suarez, Benzema...