Only time will tell Shelley. Jackmanii is not a clematis that typically gets wilt, but with most plants, you learn to never say "never" regarding anything. Cutting it back now may stimulate some new growth, but since it is an older plant and should be well established, it should recover nicely.

Another thing to consider is whether the plant wilted due to something burrowing in the ground or if the vines near the base of the plant have been cut into by gnawing rodents. Just something else to be on the lookout for.