Players dealing with Arkhan

So Arkhan wants to free Tiamat from her prison and as I understand it, the Sword of Zariel is one way to free her. What I'm wondering is what would Arkhan offer the players in return for freeing Tiamat? She can break the chains on Avernus iirc but if the players don't go for that would Arkhan try to ‘sweeten the pot’ by offering something more like the Hand of Vecna? Just curious what others have done or think about all this.