Unfortunately, this is not possible. As a design decision, all questions are DELETED from the database when you remove a chapter or level. Memory has millions of question rows, and to keep things fast, we decided to DELETE them rather than reactivate them to keep things fast for other users. (Otherwise, we would have millions of 'inactive' questions sitting in the database).
At a later date, we may be able to alter this - but it is not in the pipeline.