Well, if you don't have backups you can't restore the exact content of the directory you deleted. However, you can recreate webapplications with the following commands (assuming you used cusombuild during initial install):
PHP:
cd /usr/local/directadmin/custombuild
./build update_webapps
Assuming you didn't install anything under /var/www/html manually, the only missing part should be user files created by webmail application.
Hope that helps