I think yes, such disruptions will become more common in the future. In part because, airlines aren’t the only industry still running on mainframes, and as those systems get older, failure becomes more likely. BUT the businesses don’t see the issue, likely taking a “if it ain’t broke, don’t fix it and don’t plan on it breaking.”
Add to that, I would think the number of people who know how to both support the software on the mainframes and support the hardware are starting to dwindle.
So, at some point, a mainframe will fail (software or hardware,) and there won’t be someone who knows how to fix it (or at least not readily available.)