if(strtolower($config['server']['encryptionType']) == 'md5')
$passwordency = 'md5';
if(strtolower($config['server']['encryptionType']) == 'sha1')
$passwordency = 'sha1';
If they're SHA1, you can't convert them back to plain automatically. You should just reset all account passwords manually. :/
No, I think Gesior only supports plain passwords.