I think the real reason they bunted was Rojas looked overmatched against Gausman. He has had issues with hard-throwing right-handed pitchers. Really weak swings on hard stuff up in the zone.
I think Rojas stays up when Pache is ready, but his role might be reduced to left-handed pitchers and defensive substitution especially when Marsh is back. I think it is likely they keep both since they have 3 redundant right-handed infielders at the moment (Sosa, Castro, Wilson). One of those players is probably optioned when Pache comes back and then Marsh takes the extra September spot.
Rojas is worth it for the defense, but on offense he really got a little lucky the first time in the league and the HR against a position player and some chancy HBPs are inflating his stats a bit. He is still useful as a 600 OPS bat, but he is probably not much more than that this season going forward.