What should one do who vowed to pay money to a specific entity, but was unable to contact it after years? Is it permissible to give this vow to the needy?

The basic principle is that a vow should be fulfilled for the designated party. However, if that is not possible, it is permissible to spend it on the poor and needy. As for the vow of a gift, it is considered a vow of a permissible act, which, according to the preponderant opinion, is neither binding nor obligatory to fulfill, because what can sometimes be an act of worship and sometimes not, is not made binding by a vow.