After complete Dawnguard side, is it possible to visit Castle Volkihar with Serena?

i went back and everyone's bodies were still there

But what happen to Serena and her mother?

her mother if you go get her from the cairn will clean and fix up the garden and keep to her quarters,Serana will be at fort dawnguard if she isn't following you

Serana is fine. I kept her as my follower and she is the best. I don't want to give a spoiler so I'll just say in my game, where I sided with the Dawnguard, that nasty old necromancer is going about her business.

Thanks for not spoiling too much for me.

But one last question, if I sided with the vampires would Serana after all main quests are done, be there instead or still Dawnguard?