The missing factor is time for recovery. If an employee, even an executive, dies, it may be a problem, but probably not a catastrophe. Others can pick up the slack, a replacement can be hired and trained, etc.. You can kill the entirety of the original team and not be in dire straits, provided they die over the course of several years.

If an entire team dies at once, there's no one to pick up the slack, and no one to train replacements.

It is both unlikely that an entire team will be on a commuter bus at once, and even if they were, it is unlikely that a bus crash would kill all of them.

Plane crashes, in contrast, have a nasty habit of killing everybody on board all at once.