First, make sure there aren't broken stems causing the vine to die. The wilt is caused by a fungus that lives in soil. It enters the plant through broken stems. If it is wilt, you have to remove the stems at the base and destroy them. Then appy an appropriate fungicide if you wish. Follow directions as you need to be thorough and repeat as directed. According to a book I have, if the clematis is planted 2 1/2 inches below soil level and has built up a root crown of growth buds, sometimes the clematis recovers by itself.
I read only the large-flowered clematis get clematis wilt. so far I have been free of it, including my jackmani. Though I have seen wilt and discussed it with the gardeners at the Arboretum. Good luck.