There is a disagreement in a case where a man gives his wife a get conditional upon dying from a sickness and he is cured, is the get cancelled or not? Rav Huna thinks the get is cancelled just like a gift of someone on his sick bed. Rabba and Rava disagree because they are concerned others with think the get is only good after death and therefore will think there is a way to give a get after one dies. The gemara asks how can they override the basic Torah law that will say this is a get. In answer, they give the famous response that the rabbis have the power to annul marriages. To what extent this answer can be applied in other cases is a subject of debate among the Rishonim and in modern times as well regarding resolving aguna cases.
What is the status of a woman whose husband says this is your get from now if I die? She cannot be alone with her husband for fear that they may sleep together for the purposes of betrothal and he will be required to give her a new get. If she sleeps with another man in this period (before he dies), there is a disagreement about whether she is considered 100% a married woman or is she a case where there is doubt whether or not she is married. This would affect the punishment.