Question about Sealing Demonish (spoiler warning)

[sanjak]

Hi. I'm new to this forum and the game
I've been playing for a week, 45th day in game.

Now the question is: Will I be able to lead a Demon party again? The Dwarves want me to seal the magic portal to Demonish. But I'm leading a Demon party (which is quite great!) and don't want to lose it. My stuffs are to support Demon race and my wife is Xeona.

So why do I need to seal it? Is that the end? I still got the Dragon Labyrinth quest to go though.

Thank you very much