a part of validate_current_theme() function in the wordpress core. You can use this code under the mu-plugins folder for prevent to get death of the white screen.

theme-fixer.php

<?php
if ( get_template() != WP_DEFAULT_THEME && !file_exists(get_template_directory() . '/index.php') ) {
                switch_theme( WP_DEFAULT_THEME );
                  return false;
      }