I already wrote months ago a question about linking Lost Mine of Phandelver to another published module. By then, I hadn't yet bought the starter set and hadn't even GM'd.
I now have GM'd through the first chapter of the starter set campaign, and I really love it. I'm now sure that I'd like to buy other modules to follow on after LMOP.
In the previously linked question, Storm King's Thunder was the most cited module, and it seems pretty interesting. It was the first module I was thinking about to buy after the starter set campaign is over.
But now that I have started to play with some friends, one came with an interesting background :
His character is a monk (a woman, can't find the word for it) that before joining the group for their quest in LMOP, was guarding a temple where a powerful artifact lied, the kind that could create war over it. His character can't speak about this artifact, as it could create trouble.
I really like this background (found on aidedd.fr, a french site with a lot of translated data from the basic rules), and I'd like to use it as a plot hook for a module to string after LMOP.
So, I was wondering if there is a published module where there's a missing artifact/relic which is creating trouble by its absence.
The artifact doesn't need to be found by characters at the beginning of the module, it can even be held by the BBG. I would handwave something to link it, like if the BBG have to get it, then he may steal it in the temple or something alike.
I'd like only published modules.
If there's a module with a missing, important item, even if it's less powerful than an artifact, it's worth mentioning it too.
There are several...though they are not 'Artifacts' in the sense of being an Artifact-tier magic item, but they are unique items of significant power and importance that are causing problems and the fact that the 'wrong people' have them is central to the story, and having them be an item that used to be secured and has now been stolen is a pretty easy adjustment to make.
As requested in a comment, I'm also including the locations where these campaigns take place.
Naturally, spoilers abound. Proceed with caution.
Tyranny of Dragons
Waterdeep: Dragon Heist
Princes of the Apocalypse