The nutrients from replicated food would probably be used up by the body fairly quickly, but what about materials that aren't directly consumed? Is it possible that after a period of time they would return to whatever they were before being replicated?
The short answer is no. Once something has been replicated, it has the same atomic structure (and is essentially identical) to non-replicated matter of the same type.
There are some caveats:
Some elements are very complex and cannot be directly replicated (notably latinum but also certain high-energy elements and particles)
Some materials are replicated with microscopic voids to make them less dense.
Living biological materials cannot be easily relicated due to a lack of memory space.
It's possible to detect that a material has been replicated. There may be some kind of energy(?) residue left by the process.
But no, over time the replicated materials will degrade in the same way as their non-replicated counterparts.
There weren't anything "before being replicated". They were "energy".
There has never been any indication that replicated items are anything but 100% solid matter (i.e. stable). Otherwise you probably wouldn't be replicating spare parts for your ships!
Besides, there is no magical property of any stable material that makes it break down; that's what stable means. If they were radioactive elements then that would have been the case when you replicated them (if the replicator even allowed you to do that).