There’s probably more value in trading Fedde now. Average starting pitching in a contract year isn’t typically an extreme need at the deadline, but getting that for a whole season is likely to draw more interest. Conversely, the Cardinals do need to eat innings. But I think if Gray is truly staying, I’d try to trade Fedde now. He’s more likely to bring back a better prospect package right now than Helsley just because of the nature of their roles and their respective salaries.
But if you also trade Matz, the starting rotation may be completely up in the air going into Spring Training. Gray, Pallante, Mikolas, McGreevey and . . . You need at least 2 others as someone is always hurt. There’s lots of options (Rom, Robberse, Graceffo, Thompson, Liberatore, Munoz) but all come with tons of question marks.
Of course you could always trade Fedde for a couple other potential unproven starters.