Answer: There are several different kinds of hibiscus. Some are perennial, such as H. moscheutos. But the tropical hibiscus, H. rosa-sinensis, is not going to be perennial in areas where there is freezing weather. I am afraid the dead looking ones may have been tropicals. These are often sold as container plants for patio use and can be overwintered indoors if you want to keep them for the next year. Here is an article that talks about some of the different kinds.
I'm sorry about your plants!
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