Chances are that the roots are fine. Cut back all the dead vines to the soil and maybe it will spring back to life this year or the next.
Suzy

I have had Clematis just curl up & die in just a few days. Most will come Back in the Spring. My experience if you get them to the third year you won't have any more problems with sudden death.
George

I have found that my clematis don't like to be sprayed with anything. Mine don't even like foliage spraying of fertilizer. I would wait until next spring, it may be back better than ever.