If Rose of Sharon (Hibiscus syriacus), it is notoriously late to leaf out in spring. In my very mild winter climate, these generally show no obvious signs of life until May......sometimes later if a chilly spring.

Its not Rose of Sharon for sure, has much larger blossoms. I'd have to look at the tag to see what variety it is, but considering your comment I'll give it more time before giving up on it.

For best results here find out which species of hibiscus you are asking about. What does the labeling call them? The commonly offered kinds consist of the aforementioned H. syriacus - a hardy deciduous shrub, H. rosa-sinensis - a tender evergreen shrub, and H. moscheutos (and hybrids involving it) - a hardy herbaceous perennial. The latter species (and its hybrids) are expected to die to the ground during winter, whereas the other two are woody stemmed plants.

If they had jumbo flowers and the stems all died down readily, with only one replacement being present this year then it sounds like they are the perennial kind. And for some reason you had near total failure during the winter. But if it does seem they are this type, look at the root crowns to make sure there aren't the beginnings of other stems starting to appear, before deciding the planting has been mostly lost.

Variety is Hibiscus Paramutabilis 'Terri's Pink'

I am also on border of 8a and 7b. From what I heard, this winter was unusually cold. Hibiscus would probably survive an average winter. I plan on giving them a chance understanding I may lose them in a harsh winter. I grew them easily in FL. I hope you see green on yours soon.

That's a woody species so if most of the stems are definitely dead then something did happen to the planting. Try searching the web for "paramutabilis" for additional discussion, including what climate tolerance is expected.

Another one now has a tiny sprout. So in time more will hopefully resuscitate themselves. From everything I've read they're supposed to be good in zone 7 but I guess that nearly week-long spell in January of temps not getting out of the 20's killed them down to below the soil level. Perhaps this Fall I'll cover them with a few inches of mulch to help them out.