What happens when chemical equilibrium is restored after being disturbed?
Once equilibrium is re-established, how do the concentrations of the species compare to before equilibrium was disturbed?


Let's say it is a homogeneous equilibrium. You have to consider different cases:


The equilibrium was disturbed by changing one of the concentrations (removing or adding a substance). You can't get back to the same set of concentrations because there are too few or too many atoms.
The equilibrium was disturbed by adding solvent. Again, you can't get back to the same set of concentrations (all are lower than at equilibrium, and a net reaction in one or the other direction can't increase all of them at once).
You disturbed the equilibrium by changing the temperature. The equilibrium constant is at a different temperature will be different, so the old set of concentrations will not satisfy the new equilibrium constant.
You disturbed the equilibrium by intermittently changing the temperature (or - more elaborate - by attaching a power source to an electrochemical cell, and then replacing it by a wire shortcutting the cell). In this case, the concentrations change exclusively because of the chemical reaction (no "outside" disturbance), and they can return back to the original concentrations once the disturbance is removed.


In cases 1. and 2., however, the reaction quotient Q will go back to the original one (=K). In case 3., Q will be different.