Delete all sheets in this Google spreadsheet except for the designated sheet IDs.

deleteSheets.js

/**
 * Delete all sheets in this spreadsheet except for the designated sheet IDs
 * @param {Array} exceptionSheetIds [Optional] Array of sheet IDs to not delete
 */
function deleteSheets(exceptionSheetIds) {
  exceptionSheetIds = exceptionSheetIds || [];
  const ss = SpreadsheetApp.getActiveSpreadsheet();
  const sheets = ss.getSheets();
  for (var i = 0; i < sheets.length; i++) {
    var sheet = sheets[i];
    for (var j = 0; j < exceptionSheetIds.length; j++) {
      var exceptionSheetId = exceptionSheetIds[j];
      if (sheet.getSheetId() == exceptionSheetId) {
        continue;
      } else {
        ss.deleteSheet(sheet);
      }
    }
  } 
}