Bader and Castro are the only 2 outfielders that the team control ends at the end of the season. They would be the trade for prospects players. They may be playing well enough to get a decent prospect, that is someone with an upside more than a low leverage reliever. In all of their deadline trades Duran ad Ryan have been the only 2 who have worked out. Bader and Castro continue their success, it may well lead to a trade even if the Twins are in contention for the last wildcard spot. They might actually get their third useful piece. Yes other prospects obtained have appeared in the majors, but not as sustained success for the Twins.
If they trade from their plethora of prospects it is only because the team does not think they will be long term (the controllable years) starters.