Asara's Deal
Now that Lolth is dead, Asara no longer needs to help the party to kill her. Instead, she offers another deal, to extend their contract.
Her master is coming to these lands, and the drow were the biggest thing stopping him. Perhaps, we can sabotage him before he even arrives. She can plan for you to get entry into his lair.
If they can take out Abbadon, they will be helping her, themselves, so she is of course only indebted and at their service. She can utilize the full power of the hell forges, with perhaps a few favours ontop.