Answer
Your original message stays while you edit, cancel or leave the draft, and if replacement submission fails. For ordinary messages it is removed only after the replacement is saved, without waiting for the AI response.
On updated builds, quizzes, flashcards and checklists are updated in place. Their existing checks, quiz progress or study state stay intact. AI receives the artifact as a selected source without automatically recreating it.
Shared media remains available. The reply target must still match the one shown in the composer; if it is missing, choose another reply or remove it before sending.