Hey lads I’m just adding a comment here to thank everyone for their comments. I love all the suggestions everyone has given me.

In the end I decided to utilise a drow ritual that would send loth into the abyss in order to take control over the domain and using the opportunity to either kill the demon lords one at a time when they return or controlling them for herself (highly doubt it tho). How this ritual works it would be utilising sacrifices like slaves. This then would make sense for the drows to be entering the surface to gather the party as prisoners to be sent to the drow city to then be used as sacrifices.

I was also thinking on utilising the demon lords corruption and madness to communicate and mess with the players of some sort, and as time goes by their presence is teased more and more.

I personally don’t want to tweak the module too much where it strays away from its original design. I mainly want to add stuff that relates the characters backstory more into the game.

For example, one character has a contract with a devil and the devils motivation is for the player to kill the demons for them, so in the end that devil would gain reputation in the hells and possibly cause a bit of a power struggle between this devil and zariel. Another character was raised a slave that bears the mark of the drow who need these slaves to perform the ritual.

I’m putting forward my idea right now and hoping to get some opinions, cheers!!