Regulus Black, presumed dead for over 2 years, shows up at an Order of the Phoenix meeting with 6 mangled horcruxes and Voldemort's corpse.

How does the wizarding world move on following the abrupt end of the war, and how does Regulus come to terms with the last four years of his life?

Not on his own evidently, as his brother makes an effort to return to his life, James Potter tries to weasel his way into his heart and the friends he left behind in the name of the war aren't willing to leave him alone any longer.