I don't look at it as the "important / hard decision" from the Pep`s perspective..
Of course Rodri will be upset if he doesn't play in the final, but we all know the reputation Fernandinho has in the dressing room - even doesn't considering the fact that he is the captain now..
And what's more important, compared to Aguero - Fernandinho is in perfect form to play this game, which means that he not only deserves to play the final, but also is an obvious decision..
It's not like making a present to someone, but choosing the one from two competitors. For example it's still debatable who should play LB -> Zinchy or Cancelo and I look at this DM position in the same way..
As for the Rodri - he is the best DM in the world and I don't take seriously comments written here. Guys.. this system is built around Rodri and what we have achieved so far - is because of him, I mean he is one of the main reasons..
So Rodri is the future for sure and I don't see any reason to deny that, but right now in this exact moment.. Fern is the captain who is needed to boost / strengthen the team morale during the "times of trouble" - which will certainly happen during the Final (well.. hopefully not but you should be prepared)..
P.S Pep has 5 substitutes - so every important player will be involved if needed..