If we're talking about the death of Power in 'Chainsaw Man', my gut reaction is that reversing it would be wildly difficult and narratively fraught. The world Fujimoto built treats devils, humans, and fiends in a very specific, rule-bound way: Pochita's sacrifice to revive Denji worked because a devil literally gave up its heart to become his heart. That kind of resurrection isn't a general, low-cost trick—it's a specific, sacrificial mechanic shown once and framed as extraordinary.
Stepping back, Devil Hunters as a group don't possess a unified toolkit for reversing death. They can contract with devils, hunt them, and harvest hearts or powers, so in theory if a devil whose ability explicitly restores life existed (or if someone could coerce the Death Devil itself), a resurrection might be engineered. But those routes carry astronomical risks: losing humanity, creating a fiend, or unleashing something worse. Plus there's the metaphysical angle—death in the series ties into fear and concept-devils. Bringing someone back could ripple through that ecology in unpredictable ways. I think the story is set up to make resurrections possible but rare, costly, and morally ambiguous — which fits the show's grim tone. Personally, I prefer that tough, bittersweet edge; it makes moments of sacrifice hit harder.