PHP - include files from array only if all exist in directory

I'm trying to create a script for including (through require_once) multiple files, but I'm expecting from it following behavior:

• all file names of required files are defined as values in array
• script check if all files from array exist in given directory
• if yes, require them and continue (only if each of them exist)
• if no, terminate script and show error message (if any file is missing)

This is what I got so far but it doesn't work as it should even after adding error check (existing files are still included even if there were errors):

// Array with required file names
$files = array('some_file', 'other_file', 'another_file');
// Count how many files is in the array
$count = count($files);
// Eampty array to catch errors
$errors = array();

for ($i=0; $i < $count; $i++) {
    // If filename is in the array but file not exist in directory...
    if (in_array($files[$i], $files) && !file_exists(ROOT_DIR . $files[$i] . '.php')) {
        // ...add name of missing file to error array
        $errors[] = $files[$i];
    }
    // Count errors
    $countErr = count($errors);
    // If there was no errors...
    if ($countErr == 0) {
        foreach ($files as $file) {
            // ...include all files
            require_once (ROOT_DIR . $file . '.php');
        }
    } else { // If there were errors...
        foreach ($errors as $error) {
            // ...show error message with missing filenames
            echo "File: " . ROOT_DIR . $error . ".php wasn't found.";
        }
    }
}

I'll be grateful for help with finding right solution for this problem.