Daylilies do have the ability to re-position themselves in the ground.
Only one researcher has looked at this but he has looked at it in some detail. His scientific article can be downloaded and read from (all one line)
http://www.uni-vechta.de/filea...
That ability may work best when the crown is small rather than when there are many fans and the crown is large. There will probably be differences between cultivars in whether they re-position themselves and how deeply, etc. The type of soil and other factors may also influence the behaviour of the roots.
I am in zone 4 and some daylilies here also pull themselves deeper but unfortunately not necessarily when it would have saved them (after being frost heaved).
