First thing is to inspect the teeth of both sprockets. If there is no visible wear at all, and the teeth look fresh, then more than likely the chain is still within limits on the pitch.
When the chain pitch changes, it will start to wear on the sprocket teeth.
The "rule-of-thumb" for changing the whole thing out as a set is based on the fact that most riders have a bad habit of not changing things out until the chain has stretched past limits and started to damage the sprocekt teeth.
Learn the proper way to measure your chain links. If you keep an eye on your chain, and not let it elongate past ~1.5% of what if was at new before taking it off, then you can continue to use the same sprockets. If there is no visible damage at all on the teeth, why would you not be able to use them? You CAN use them, and continue to do so, AS LONG as you keep an eye on your chain.
If you find that a bit more maint. than you want to perform, then wait till you see the teeth start to hook or point, and change out the whole schmear.