1. When you pass your FMS descent point for your destination the Airbus gives you a tone and CAS message along with VNAV bars on your PFD display.
2.When you pass your last fix in the FMS (their destination in this case) the Airbus autopilot goes into heading hold with a tone and multiple CAS messages along with the fact that your little digital plane is flying off into the abyss on your big EFIS NAV display.
3. In the case of a missed frequency hand-off ATC would have called on 121.5
4. The airline has a similar system to AFIS to contact the crew that went unanswered.
5. ...and if you miss all that, 78 minutes of no calls from ATC didn't arouse their curiosity? Hope for an FA to send you a signal..