Must an endowed donation fund that was unintentionally lost after being used for its designated purpose be guaranteed?

If the box was lost without any negligence or dereliction on your part, then you are not liable for it. However, if you were negligent in safeguarding it, then you are liable for it and for the funds it contained, if found, because you were entrusted with it. A trustee is not liable except in cases of transgression or negligence. The hand of trusteeship is not liable except for transgression or negligence, whereas the hand of guarantee is liable in all circumstances. Therefore, as long as you used the box for the purpose for which it was endowed and no transgression or negligence occurred on your part, then you are not obliged to guarantee it. And if you bring another one, it is better for you and further from doubt.