On 22/05/2020 19:06, Jeff Layman wrote:
Snipped

Thank you, I assume that the plants I ordered last October must have had
the disease.

Not necessarily; in fact it probably very unlikely.

From
https://en.wikipedia.org/wiki/Phoma_clematidina#Disease_development:
"When spores of Phoma clematidina land on a leaf of a susceptible plant
under the right environmental conditions (moisture, temperature 15 to 25
°C), they will germinate within 6 hours and infect leaf tissues directly
or via leaf hairs. "

If your plant is still alive on Sunday then it hasn't got clematis wilt.
Even if it has, and you cut it off at ground level, it will recover. I
posted here two weeks ago "Clematis wilt - early this year" that my C.
viticella 'Margot Koster' had got wilt and I had pruned it to ground
level. I just checked, and it has a new shoot about 25 cm high.
Remarkably, it looks as though the top bud will be a flower rather than
a leaf.

Thank you for your advice. I've just checked again this morning, all
the flowers and leaves on one side are fine. I am wondering now whether
the wind snapped one of the stems. Maybe I'm just living in hopes!;-)
--
I'm a sew and sow!