That's debateable. The playing games during company time would be considered misconduct. For that they'd have to go through the usual warning procedures. The failure to maintain the backups, which is a business critical function, would be considered gross misconduct. The "gross" in gross misconduct infers doing something illegal or something that could be considered a breach of health and safety. Accidentally forgetting to check the backups would be misconduct, deliberately not checking the backups is gross misconduct.