Everything. Your account itself, and all of your writing — every project, every chapter, every interview answer you spoke, every write-up GlideProse produced from them, and every draft you imported. All of it is removed from our servers when you confirm.
Nothing is kept back, there is no separate archive, and there is no retention window that holds your writing after deletion. Your email address goes with the account.
This cannot be undone. If you want to keep your manuscript, export it to a Word document first — open the project, go to the manuscript screen and export. The file is saved to your device and is unaffected by deleting your account.