A Microsoft Support case pointed me here in the hopes someone here has an answer to this.
I'm looking for a better way to delete document libraries that have 500,000+ items, to some with over 1 million items. You cannot delete the library because it's over the 100,000 item threshold for deleting a library as a whole through the UI. My work-around so far is I've written a PowerShell script that goes through and deletes items one-by-one until it gets under 100,000 then I can delete the library. Not great, but at least it's automated.