Castlevania can live on in other franchises and stories and stuff. it's very easy to create similiar themed content without plagiarizing.
look how other series have inspired others to make original yet very similiar concepts
a simple example is Demon's Souls, Dark Souls and Bloodborne. them coming from the same developer is not the point, each of those games could have been invented from entirely different sources, and still share things in common. and the fact remains that despite being similiar, they are not the same IP. Dark Souls is not Demon's Souls 2, Bloodborne is not a Dark Souls.
So really, things like Castlevania can be adopted and reinvented in similiar and superior ways. you can see how even the hunters vs vampire/etc. theme exists in all sort of independent stories and games.
so Castlevania is not the only source the concept can live in. anyone can create spiritual successors to Castlevania in tons of ways. the concept in itself has infinite potential.
Castlevania had its era, but its fans can create independent masterpieces that are not called Castlevania. It's very possible to reinvent and surpass Castlevania, and that in itself would make something a worthy inspired series. So with what was experienced and absorbed from Castlevania, its fans can expand Castlevania's legacy in different creations with different unique titles.