Background Story at https://en.wikipedia.org/wiki/United_Breaks_Guitars
Wow! I pity the person in charge of PR at United right about now. Oh wait! that would be me for this scenario. So what would I do?
no thorough investigation needed at this point. There are a number of real complaint and equally the same amount of disgruntled customers. I will set up a crisis communication and resolution committee. We will reach out and apologize publicly, taking full responsibility of our mistakes. We will inform the public that we are intensifying efforts to correct those mistakes and make sure they never happen again.
The team will attempt to communicate with concerned customers, and offer ways to soothe their angst about the United brand(new guitar, free or discounted flight, etc.)
For the employees at the middle of these crisis, disciplinary actions will be taken to the full extent, meaning firing where necessary. Those who are retained will have to go through intensive training and evaluation in order to return back to work.
I'd be tempted to want to re-engineer a positive viral video but if all that we have strategized work according to plan, a counteracting viral video is unnecessary.