Neville never felt lonely in the castle anymore.
Severus and Harry never moved out. Not even after the war ended. Not even after all remaining Death Eaters were captured and sentenced to prison. Not even after Neville got married to a witch he had met on a Herbology conference. Not even after Harry got married to Hermione.
Currently, there were two little Longbottoms running around the halls, screaming their lungs out, making faces at old portraits, and teasing magical plants in the greenhouses. There was a little Potter-Granger always toddling around after them, as quickly as his short fat legs allowed him. Usually, the whole group was followed by one proud parent or honorary 'Grandpa'.
Life was good.
Epilogue
The End.