It’s really not such a stupid question, however, it would require Congress to advise & consent for the selection of a new Chief Justice. So highly unlikely that a current Chief Justice would be replaced and the current Chief Justice revert to being an Associate Justice. The Constitution only mentions a Chief Justice on the Supreme Court with regards to presiding over an impeachment process. But the question then becomes, who presides if a Chief Justice is the one being impeached? 8>)