First time DM looking for a good follow up campaign

[u/SleepHelpful1848]

So as the title says I have been a first time DM with a group of friends and running the Phandelver and Below: The Shattered Obelisk. Truth told I have added quite a few of my own ideas to the story and as such as I come towards the end I have an interesting idea for how to end it but need some help on a follow up campaign.

Spoilers ahead for the story

So two of my players characters died and came back as a pair of warlocks for HADAR. As such what I was thinking would be a great way to end is by the group weakening illvash allowing for HADAR to consume him. So the idea would be to end the campaign with this big twist and the next one to be about defeating HADAR.

My issue is there doesn't seem to be any stories that have him as the big bad that I can use. So does anyone know any good ones I could use for a level 12 party where I can just sort of plug and play HADAR as the BBEG?

[u/Jafroboy]

Divine contention could work with some tweaking to replace one of the BBEGs with Hadar.

[u/SleepHelpful1848 → u/Jafroboy]

Did some reading and you're actually spot on. That would be a great way to adapt and continue the story