I found interesting post on Social BioWare:
Is there any chance we will finally get to see the resolution to this loose end in DA III? If not in the main plot, then at the very least in a passing reference made by other charachters, or in a lore book found somewhere along one's adventures.
Hmm. How can I put this?
The results of the Dark Ritual, if it occurred in DAO, will have more than a passing reference in DAI.
Beyond that, you shall have to wait and see.