I think that is kind of a bonus for Rojas to only worry about hitting, no doubt. But as sooner as he's cleared to throw he'll be out there.
Of course they could carry Mercado and just let Rojas play every day in AAA for a couple of months. But I agree, he is the most logical replacement for Wilson if you want someone who can actually play the OF, versus, one big PH (which Kennedy can give you).
My guess is unless there's a minimal trade offer for him Clemens breaks camp just to keep him on the roster, much like Altherr did that one year when he was out of options and Quinn got hurt (he was eventually DFA'ed in mid-May).