Generally, teams don't demote guys 2 levels, even to learn another position. I actually think Harrison's fate is tied to Alvarez, the same as Hague's.
This stuff of playing guys out of position, to help them become more versatile, is fine for ST. But when the bell rings, I think you'll see guys more in their usual positions. So:
If Alvarez starts at 3B for the Pirates, McGehee platoons with Jones at 1B. And against some of the NL's toughest LHSP, you may want to sit both Jones and Alvarez, and stack as many RH bats in the line-up as possible. Creating a need for a RH bat, that can play 3B at least semi-adequately. Making the bench:
McKenry
McLouth
McGehee
Navarro
Harrison
However:
If Alvarez goes to Indy to begin this season, McGehee plays 3B FT. And Hague platoons with Jones at 1B. Hague being a rookie and all, they'll want some protection for him, in case he falters. Creating more of a need for Fox. Making the bench:
McKenry
McLouth
Hague
Navarro
Fox
I think Navarro comes north, regardless. He's the only one left standing that has the glove to back-up the MIF. And Harrison's, Hague's, and Fox's fates are tied to what happens to Alvarez, and consequently, whether McGehee plays full time, or part time.