If a sudden incident may have lost most of your office or factory manpower, then how can you overcome this adverse situation?

That you've already anticipated the possibility of such a risk to take place, best management option should aim to reduce the impact of this risk by sharing it. management options such as buying business interruption policy would be valid other options as to sign contracts with another company in quite similar industry to provide you with back up in such an event in return to same thing for them.

you can offer raises and promotions to keep the rest of employees motivated & carry on the work.