No a daylily cannot revert back to one of its parents. There are a few daylilies that have some variegated leaves and those are known to be unstable - that is some of the fans can be all green. However, that is not reverting back to one of its parents.
If a daylily is allowed to set seed and the seeds are not removed then they can fall to the ground and germinate into a new daylily plant. That plant will not be the same as its parent but may be quite plain. It may also be quite vigorous and outgrow its parent as time passes. If that is the case then after a few years only the seedling will be growing and flowering and then some may look at it and consider that it looks old-fashioned and like an ancestral daylily. But the original plant did not revert; it was more or less killed by its offspring and the offspring was not a parent or ancestral daylily.
