When my father died, my mother-in-law received the usufruct of the entire estate, which consisted mainly of liquid assets. Today, she has just died, and the liquid assets have disappeared. What can I do to recover these sums?

When the spouse receives the usufruct of liquid assets, we speak of quasi-usufruct, i.e., a usufruct (right of use and enjoyment) of a thing that is consumed when used (money). In practical terms, the spouse has the right to spend the money, but is obliged to return it on his or her death. You then have a restitution claim on your mother-in-law's estate. However, this must be sufficient, otherwise the money cannot be recovered.