All of my helianthemum are looking sad this year. They typically stay evergreen (if a bit ratty) over winter, then put on a flush of new growth in the spring. I usually shear them back at that point to shape them and keep them tidy. This year, they just looked like dead sticks with only a small amount of growth at the tips. I sheared them back really hard (to about 3") hoping for the best. Most are very slowly recovering, so hopefully they will survive. Must have been something about the winter they didn't like - we got quick freezing temps in the fall, then had some dry winter months, so could have been either or a combination of both.