People, don't be so delusional! This company has existed for well over a century, many, many years before you worked here and will continue to exist long after you're gone! NOBODY is indispensable no matter what your job function is within the ranks! The work will get done one way or another, just not by you or anybody else that leaves with their irreplaceable knowledge! Don't kid yourselves!
If you don't realize @leh+1jiMp585 is right, you're just fooling yourself.