When you delete a question students have already answered, it disappears from the quiz and the course player and is never served again. It’s kept, with every answer given to it, in Reports, where it’s marked Archived.
That’s on purpose. The answers are your record of what students did, and deleting a question shouldn’t delete the evidence.
A question nobody has answered yet is removed outright. If you put an archived question back, its answers come back with it.
Surveys work the same way. And with Pro, an essay answer to an archived question stays in the grading queue with an Archived badge, because the answer is real and still needs a grade.
A question in Reports says “(Untitled Question)”
That question was saved without any text at some point. Its answers are real, and they’re kept.