Then it would be a bad working environment, but for another reason. Companies should assume that anyone can be run over by a bus at any time and plan accordingly.
This doesn't seem reasonable. If you assume anyone can be run over by a bus, most ways of mitigating that risk involve some recovery time. If it takes 4 hours to recover that person's work and get up to speed, the company has planned accordingly, but it's still extremely inconvenient to lose half a day because someone didn't show up to work.
