First. Check all tables and see if tables use any prefix. Is it possible that someone changed configuration to remove prefix
Look in system/config.php
define('DB_PREFIX', 'ac_');
If this is not the case:
Check backups. Go to admin/system/backup/ directory or check admin -> system -> logs -> install/update
If there is any backup you can restore just this table
Finally, you can run below SQL:
DROP TABLE IF EXISTS `stores`;
CREATE TABLE `stores` (
`store_id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(64) COLLATE utf8_bin NOT NULL,
`alias` varchar(15) COLLATE utf8_bin NOT NULL,
`status` int(1) NOT NULL,
PRIMARY KEY (`store_id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_bin AUTO_INCREMENT=0;
INSERT INTO `stores` VALUES (0,'default','default',1);