How can I disable "Delete the account and its content"?
You can implement hook_form_alter() in a custom module or theme to either remove the radio button entirely, or disable it which grays it out. You'd need to add additional logic to check the role of the user and disable it appropriately. I've shown both examples in the code example below, just uncomment the one you want to use.

function mymodule_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  if ($form['#id'] == 'user-multiple-cancel-confirm') {
    // Set '#access' to FALSE to remove the radio button.
    // $form['user_cancel_method']['user_cancel_delete']['#access'] = FALSE;

    // Set '#disabled' to TRUE to disable the radio button.
    // $form['user_cancel_method']['user_cancel_delete']['#disabled'] = TRUE;
  }
}