It's nice that everyone is so concerned about how long the battery backups last before the generators kick on....
Let's take a minute to discuss site redundancy and geo load balancers.

There is NO reason an enterprise of this size should be hosed by a power failure at a single location. In 2016, that is literally inexcusable. Here's what happened (another IT guy here, using his crystal ball).

Multiple solutions integrators and IT service providers have sent proposals to Delta with fixes for this for YEARS. YEARS. Someone at the top has decided that the cost outweighs the risk, and the papers have gotten lost in the pile.

Well guess what. That person will likely no longer be employed shortly. Delta will shell out 5-50 million in network redesign, app compatibility/lift and shift etc.

Here's a hint, Delta. If you want to boast about a BILLION dollars in profit, and how you distribute earth-shattering profit sharings, take the time to invest in your infrastructure first. Today cost you more than any day/event in the past decade, and it could have been avoided.