I'm trying to think of a high performing player in contract year moved at deadline who didn't stay. Only recent one that comes to mind without research is Manny Machado. The Dodgers gave up a pretty decent package of prospects who all flamed out with the Orioles. Go look at the prospects rankings on Machado trade and I would take 75% of that happily.
It's hard to say they all flamed out, and that was hardly a decent package considering that system was insanely loaded. I remember seeing Rylan Bannon that summer. He might have been the fifth or sixth best player on their high-A team. And he still hit decently at AA and AAA in 2019 and just turned 25. Pop got hurt and might or might not be fine - he had Tommy John and then got Rule 5'd and is now in the majors with Miami. Diaz is the big disappointment.
As for other deals like that, Zack Greinke got rented by the Angels and didn't stay; Darvish was rented by the Dodgers in 2017 and didn't stay; Toronto rented David Price for about 14 minutes; the Cubs rented Aroldis Chapman for maybe 17 minutes; Jon Lester once pitched for Oakland. Even the Nats rented Melancon, who didn't stay.
