Posted: 17/07/2015 at 15:36
Did it die from the top down or the bottom up?
Usual reason for Clematis failing like that is damage to the stems at the base. Snails adore stripping the bark of at ground level and that stem then dies back. When that happens the things dies from the top down. Wilt kills stems from the bottom upwards.
In either case, cut off the dead stems , mulch with organic material and wait. We have had Clematis sulk for 2 years before re-growing.