This almost happened to me last year. I overestimated how long it was going to take me to get to LGA and arrived at the gate over an hour early. Took a seat near an outlet and started working, only half-noticing that there were very few people in the gate area. About 20 mins before the scheduled departure, I was surprised to hear my name being paged to the gate directly across the way. Apparently there was a gate change after I cleared security (and after the T-1hr AA txt) that I didn't notice.
Admittedly, I should have been more proactive in investigating why there was no one at the gate 30 mins prior to departure, but you would think there would at least be a local announcement or a follow up txt regarding a gate change within T-1hr.