The typical recommendation is to cut the vine back to below any sign of wilt and treat as normal (regular watering, mulch, fertilize as necessary, etc.). Wilt is seldom fatal and most vines will outgrow it in time although they can appear to be dead (or close to it) for several years before springing back to life. FWIW, most of the clems in my garden were those returned to my previous nursery for refunds due to wilt. And I have never, ever, permanently lost a clematis to wilt in all my years of growing them (lost them due to a couple of other reasons, tho).

Thanks.