Can the floor be brought back to its original shine if it gets dull?

Yes, and it will never be as involved as the initial process. Normally it will only take a pass or two with resin steps to reach the end result desired. Which also means that it never cost as much as the original job, unlike epoxy coatings, urethane coatings or VCT which always cost the same or even more than the original job due to the labor required to remove the old surface.