It's normal for a plant to "stall" for a bit after being hit with spring sickness, but you're in a pleasant climate, and the plant looks big and strong otherwise, so give it some time. If the plant has to generate new growth from a dormant growth bud, it could take quite a while to show up, but most of the time I see this, it recovers and continues to produce new leaves from the center.
I suspect that in most of the cases where spring sickness has killed a daylily, it was either in a much colder climate, and the plant was under stress from winter, or it was in an extremely hot, humid, near-tropical climate where fungi can really thrive.
About how many hours of direct sun are these plants getting now?
