Segura is not the one who gets to decline, that's up to the Phillies. And it's still a fool's game to pay him like he's the exception to aging if you don't have to. He could end up having a season like 2019 (though by his own admission he was not taking care of himself at all then) or he could miss two months with another injury (this year was bad luck, granted, but older players also heal more slowly and recover less convincingly).
Hoskins just doesn't have much trade value. He's a RH DH due for a big salary bump who is about to hit free agency. His bat plus the comp pick is probably worth more to the Phillies than any trade return, unless you see the primary value of the trade as simply freeing up the $ and playing time. You can certainly make the case, though
Castellanos/Hall would make more sense at 1B as Schwarber is still probably a better LF than Castellanos and can't platoon with Hall at 1B or DH.
I also think if Harper is going to end up missing a couple of months they probably have to keep Hoskins.
My guess is our shadow GM (Harper) will still get the guy he wants (Turner), or else our real GM (well, President of Baseball) will convince him Bogaerts is the guy. Just a question of where they actually play.