It pretty much goes no where, unless someone continues to push it. Since the original complainant dropped the issue, the easiest thing to do is to administratively close the file.
This happens often in contentious divorce and custody cases. Often both parents file CPS claims against each other, allegations of all kinds of abuse. It actually "weaponizes" CPS in a "game" of custody, rather than actually being legitimate child abuse. Closing a file in those cases is the best option, unless a judge orders a home study or other court mandated actions.