I have had culms completely defoliate and then re-leaf, so all is not lost, necessarily. I've also had culms with the top half dead and the bottom bushy, so I pruned off the dead part and left the bottom since I had a lot of other full-size culms adjacent.

It won't hurt to give them another month or two to see if they become presentable. The ratty leaves should drop off (or you can pick them off), and you can always prune out stuff that still looks bad later in the summer.

I agree with kudzu. I'm not surprised the Golden (Phy. aurea, right?) topkilled as it's not hardy enough, but the Yellow Groove should be one of the hardiest. Was it a young plant?

True, yellow groove is one of the hardiest, what other ones do you have that are doing better?