Musar do Liczb 35:28

We find that such is the case even when the souls in question had not been separated from their bodies through murder. A soul which is "exiled" may be released from such exile as a result of the death of a great person, i.e. a prominent צדיק. The Zohar Mekor Chokhmah finds an allusion to the statement of our sages that "the righteous may be granted children when they have died, though they had no children during their lifetime," in the words כי בעיר מקלטו ישב עד מות … "he has to remain in his city of refuge until the death." [This means that as long as the soul of the righteous was held captive by its body it could not become a parent. Ed.] This demonstrates retroactively that all G–d's actions are based on truth, and that He shows His mercy to all. A soul that is separated from its body and does not have any "clothing" to accompany it to the higher world (since it did not leave children behind in this world), and therefore lacks a גואל needs to remain for a while in the "city of refuge," i.e. a place where souls hover until the death of the High Priest who is the Torah scholar. He does not require a גואל. If the High Priest leaves a widow and no children, the levirate marriage rules do not apply to such widow (in the sense that she need not enter into a marriage with a brother of her late husband in order to perpetuate his name on this earth). If she does so nonetheless, it is for the benefit of other souls who are homeless in a region between this world and the world to come. These souls await the time when they can be suitably "dressed," in order to proceed to their ultimate destination. The High Priest widow's late husband's "continuity," שם, has been maintained even though he did not leave behind physical issue. So far the commentary of the Zohar Mekor Chokhmah. [The source in the Zohar for this seems to be in Parshat Vayeshev on 38,8, where Yehudah instructs Onan his son to marry Tamar the widow of his brother Er. Ed.]