What is the method for absolving oneself of responsibility for workers' wages that they were unable to collect due to unforeseen circumstances, and in the event that their number is unknown or they cannot be reached? And is it permissible to use Zakat for this purpose?

It is your duty to strive to deliver the workers' rights to them through all possible means. If you are unable to find them and despair of doing so, then give their rights as charity on their behalf, and exert effort in estimating the amount so that your responsibility is cleared. There is no sin upon you for delaying salary payments if that delay is not due to any negligence on your part.