You can always prune out dead, diseased, damaged, or rubbing wood as soon as you see it (any time of year). The question is whether you know for sure whether it's dead. If there is no green in the stem when you scrape down into the cambium, then pruning now would be fine.

They bloom on old wood. If you prune now, you will lose the spring bloom. But if they are in bad shape, you may not get one anyway. I lost 2 for the same reason. I never had to water them before and this summer was just brutal. These plants have been in the ground for over 7 years, so I thought they'd be ok. WRONG!!!

Buford, it really was brutal, wasn't it? Sorry you lost a couple too. Thanks for the reminder about blooming on old wood. I was going to trim the rest of the row while I was at it but I'll hold off until Spring.

Brandon, thanks for the suggestion to scrape to be certain they're dead. I just checked and it's only the top 1/3 that's dead. The middle part has no leaves but the stems are still green.

Thanks again to you both. I'll let you know how they're doing in the Spring.