Is it possible to check whether an identifier exists in a storyboard before instantiating the object?

As Tom said, the best solution to this problem is the try-catch block:

@try {
        UIViewController *newViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"identifier"];

    }
    @catch (NSException *exception) {
        UIAlertView *catchView;

        catchView = [[UIAlertView alloc]
                     initWithTitle: NSLocalizedString(@"Error", @"Error")
                     message: NSLocalizedString(@"Identifier not found on SB".", @"Error")
                     delegate: self
                     cancelButtonTitle: NSLocalizedString(@"OK", @"Error") otherButtonTitles: nil];

        [catchView show];
    }

I hope it helps! even though the answer is really late.

You can use valueForKey: on UIStoryboards. UIStoryboards have a key called "identifierToNibNameMap", its value is an NSDictionary with the UIViewControllers in that storyboard. This inner NSDictionary uses the viewcontroller's names as keys so you can actually check if a viewcontroller exists in a storyboard with the following code:

if ([[storyboard valueForKey:@"identifierToNibNameMap"] objectForKey:myViewControllerName]) {
    // the view controller exists, instantiate it here
    UIViewController* myViewController = [storyboard instantiateViewControllerWithIdentifier:myViewControllerName];
} else {
    //the view controller doesn't exist, do fallback here
}

Note: Apple has been known to reject apps that query the underlying properties of cocoa classes using valueForKey:. These underlying properties could change at any time in the future, breaking app functionality without warning. There is no deprecation process for these things.

@Kevin's solution works. Here is a pretty the same piece of code for Swift 3 as function, that I am using in my code:

func instantiateViewController(fromStoryboardName storyboardName: String, withIdentifier identifier: String) -> UIViewController? {
    let mainStoryboard = UIStoryboard(name: storyboardName, bundle: nil)
    if let availableIdentifiers = mainStoryboard.value(forKey: "identifierToNibNameMap") as? [String: Any] {
        if availableIdentifiers[identifier] != nil {
            if let poiInformationViewController = mainStoryboard.instantiateViewController(withIdentifier: identifier) as? UIViewController {
                return viewController
            }
        }
    }
    return nil
}

Use this function as follows:

if let viewController = self.instantiateViewController(fromStoryboardName: "YourStoryboardName", withIdentifier: "YourViewControllerStoryboardID") {
    // Here you are sure your viewController is available in the Storyboard
} else {
    print("Error: The Storyboard with the name YourStoryboardName or the Storyboard identifier YourViewControllerStoryboardID is not available")
}