If you were getting investigated by the IRS, and you gave the IRS the answers that they have been giving the public over Lois Lerner's and others' lost emails, do you think that the IRS would accept your answer?
By the way, a system crash that makes a hard drive totally unreadable is just vanishingly rare nowadays. It is possible to corrupt certain system files in the root that will make it impossible to log on to the computer or access the hard drive files normally, but they are still there. Something with the hard drive's motor or read heads could fail, but the data is still there. Even if you highlighted every file in your hard drive and hit the delete key, they are still there. When you hit delete they are taken out of the file directory and may get overwritten if you add new data to the computer, but without special software, it is actually hard to totally delete files (this is why you have to be careful when you donate or dispose of computers). It actually can take the better part of an hour to really remove all files from a hard drive so that they are unrecoverable.
Given all this, I think the odds are that 6 or 7 computers of a group of senior leaders in the same office all crashed at roughly the same time in a way that wiped out all the data from their hard drives such that all data would be unrecoverable is simply beyond credulity.