Apple ID locked. Rescue email no longer exists and security question failed

My 80 year old father cannot remember his Apple ID password for his iPad. The account is now locked due to too many failed attempts. The security question also failed and the rescue email address no longer exists. What are the options here to unlock and reset the Apple ID password. No other Apple devices held. Any assistance would be greatly appreciated. He is used to using the iPad and I am concerned we may need to purchase a non Apple tablet if this can be resolved. I