Some are, in the form of excrement. Most are not, because they're released as heat with the animal moving around and maintaining homeostasis. It's the same for us except all our excrement ends up in a landfill.
Exactly, what if the animal just dies without being eaten... are 100% of it's nutrients wasted? Or did it lead a full life and return from which ot came?
It's relatively rare that living organisms die without being part of some further biological change, though that does happen. Fossil fuels are formed through lack of biological decomposition, as are precursor materials: peat bogs, kerogenated biomass, abiotic methane. Deaths in desert, arctic, or alpine conditions may simply dessicate and degrade rather than being eaten.
The entropic channel may pass through biological mechanism, but there's no obligation that it must.