I do not know the plugin but following function could solve your problem,
Add the following code-snippet(function) to functions.php.
After creating the new admin, use the credentials as given by yourself.
It does not recover the state of wp nor your admin user but this function creates a new admin user. So you are able (only when there is/was no other reason then that plugin you deleted which maybe causes all trouble) to login as admin with the capabilities which belong to that user role.
function add_new_admin_account_195142(){
$login = 'newadmin'; // Create/Use an unique name
$passw = 'newpassword'; // Create unique pw
$email="[email protected]"; //Use unique email address
if ( !username_exists( $login ) && !email_exists( $email ) ) {
$user_id = wp_create_user( $login, $passw, $email );
$user = new WP_User( $user_id );
$user->set_role( 'administrator' );
}
}
add_action('init','add_new_admin_account_195142');
I have no idea what the reason was/is that a plugin would/could do such so I am not 100% sure if you succeed.(normally it should do the trick imho)