Miranda's value to the Twins at this moment is that he is an acceptable option at third base and first base. It is not like you hand a guy a first baseman's mitt and say "you're a first baseman". Other infield positions have some commonality, probably most is third base, but there is stuff to learn at each position and there have to be some skills. Kirilloff, for example, has long been projected as a good or better first baseman, while someone like Brent Rooker wasn't (despite that being his primary position in college). The Twins have identified Arraez as an infielder and rather than have him in left field, they have decided they would rather have him being an undersized first baseman. The word is that Gary Sanchez is taking grounders at first. Maybe this is a "break glass in case of emergency" thing or maybe they'll roll with it in games. I also noticed that, rather than move utilityman Nick Gordon to third base when Correa pinch hit for Miranda, the Twins used their last bench move and put Urshela in the game. That tells me that, in their minds, Nick Gordon isn't a third baseman. It would figure that if Miranda is sent back to the minors, there would have to be defensive flexibility both at third and first base.
This kind of stuff fascinates me, like the fact that Kepler hasn't played left field, and the pecking order between Larnach and Kirilloff between left and right field (if both are manning a corner OF spot, it is Larnach is left and AK in right). Nick Gordon is now deemed an acceptable option at short and second and left and center, but has only played a few innings in right. The other day in Oakland, they brought Miranda in to play first base and moved Arraez to second rather than giving Miranda a couple innings at second.
Circling back to the OP, Royce has gotten to stand at third and in left, hurray. Hopefully, he is working on alternate positions before the games. He's a great talent and I'd love to see him back in Minneapolis without another Correa injury.