This is the reason why I stay in the airport lounge if you have access to one or if not its worth purchasing a Day Pass on a Delayed Flight over 2 hours. When your flight is delayed the lounge can call down to the gate to get an estimated time of boarding.

In your situation I would have stopped by the gate to get an estimated time of the new boarding time as I do when my flight is delayed. Then 20 minute before the new boarding time I am waiting at my gate and I have never missed a flight.

To me the lounge is the way to go because I am able to ask the front desk staff about the new fight and they can rebook me to a new flight if there is a need. To me even if I had to pay the $50 I would do so in a heartbeat.

Quite frankly the OP needed to have listened for announcements of the new boarding time and check the Flight Information Displays. I am sorry but they would have announced that your delayed flight was boarding.

I have heard many times for Passnegers X and Y to come to the gate as the door will be closing in 10 minutes and your reservation will be cancelled and your seats will be reassigned, Either the OP was listening to his or her music or was in a secluded area away from flight announcements.

EVen in the lounge it is your responsibility to keep track of your flight even by asking the front desk staff for any updates or "will my flight be boarding on time? when checking into the lounge.