How can a trust, represented by a sum of money collected from female students and not returned to them, be restored, given the loss of names and the dispersal of the students, and is it permissible to donate this money with the intention of restoring the trust?

If you are unable to identify the students to whom you owe money, you should give the amount in charity on their behalf, and your obligation will be discharged thereby. Ibn Taymiyyah said: "If the owner of money cannot be identified, it should be spent on the welfare of Muslims according to the majority of scholars. So, if a person despairs of identifying the owners of usurped property, deposits, or pledges, he should give it in charity on their behalf or spend it on the welfare of Muslims." In "Kashshaaf al-Qinaa'", it states: "He should give it in charity on behalf of its owners, on condition that he guarantees it to its owners if he comes to know them. The sin of usurpation is thereby lifted from him, and the reward is for the owners of the money. This includes pledges, deposits, all other trusts, and unlawfully acquired wealth."