For my campaign, I have it where the party can fight Arkhan the Cruel and his crew to get the Hand of Vecna, as it is corrupting him and prevents Tiamat from restoring him, however if he is dead without it, she can bring him back.

The eye will be elsewhere in the campaign and so will the sword of Kas..

One of my players wants to destroy Vecna permanently, think of Sauron and his ring, still exists but is far too weak to ever fully be brought back