If your replicator needs a literal bitmap for every atom possible in an object. You would need to store 7 bits (maybe future proof it with 8 bits in case we find a lot more elements) for every atom in the object.
Then it's simple multiplication to calculate atoms * 8 bits
Then we need to store the location in 3D Space of each atom. The actual unit of measurement is whatever you want. Then pick a number of bits to hold that number, and multiply again.
I can't help you more than this though unless you can say how many atoms are in an A-10 Warthog and their groupings by element.
And for the gradual decay, just say the spatial measurements aren't exact enough, so eventually it falls apart.