I have to point out to you that your choice of the word "hostages" is akin to calling firemen hostages who leave the Thanksgiving table to respond to a five-alarm fire with people trapped on the upper floors.
I can understand how you're thinking, based upon that a lot of people don't understand something about drilling oil. In oil drilling, emergency situations come up more often than you know. I have several cousins offshore at the moment, including a rig manager, my uncle worked his whole career for Texaco, my grandfather worked his whole career for Texaco, and my great-grandfather was present at Spindletop in Sour Lake, Texas, when the first huge strike was made in the early 1900s that made Texaco.
Deepwater Horizon blew out due to unmanageable pressure coming from under the ground. What allows you to drive your car, if you drive, is that men and women are working tirelessly, 24/7, to manage incredible pressure from inside the earth's crust, without a Deepwater Horizon happening once a week.
That mammoth pressure has to be managed vigiliantly, 24/7, through a series of valves.
The pressure is not constant. As the drill bit proceeds, core samples are brought up, and examined by geologists such as Mr. Shunick to determine what sort of stratum the bit is getting into. Hitting a different stratum as the bit goes deeper can make the underground pressure change suddenly and violently, and result in a blowout. The earth's underground pressure doesn't respect high-school graduations, weddings or funerals. Mr. Shunick is a specialist - not a roustabout. There aren't as many Mr. Shunicks to go around as your everyday roustabout.
It is part of Mr. Shunick's job to be available to fly out to a rig in a hurry to evaluate a rig whose pressures are changing, so as to prevent a disaster.
If that rig needed him - and if that particular company had only one geologist on call - then Mr. Shunick may well have been needed immediately to look at the samples - to prevent a blowout of the well.
Even had he asked for the day off... the earth doesn't care. That's his job.
I hope that helps you understand better, and also helps you realize why questioning Mr. Shunick's absence at his son's graduation reflects more on his job than on his character or choices.