They can probably still ride this out for another six weeks (could be another three before Turner's back anyway) because the team is winning, the schedule is still reasonably soft until July 1 and this past week's evidence aside, the need for a PH or key tactical substitution is still pretty rare (and it was just the other day that someone here was arguing Clemens shouldn't be coming in for Sosa). But they also had the flawed belief that Merrifield could hit RHP (or rather, the flawed belief that he could still hit at all).
I feel like the call has already been made on Rojas. Especially since Pache wouldn't be better (he'd be adequate and a placeholder to allow Rojas to develop, but I think Rojas has shown he can develop while playing in the majors, without hurting the team when he hits bumps. No different than our 3B for three years). But no question he has struggled, it would not be the end of the world if they gave him a pause (which also happened to Bohm and Stott).
