Answer: The patio hibiscus often sold as a container plant, Hibiscus sinensis, is a tropical plant and will not tolerate a cold winter. The tropical hibiscus needs to b brought indoors for the winter, preferable so it does not experience temperatures below about 45 to 50 degrees in order to keep the plant as healthy and unstressed as possible. So if that is what you have, they are most likely dead.
Hibiscus syriacus (Rose of Sharon), however, is a very cold tolerant and hardy shrub hibiscus and there is a chance it would have survived winter in a container. If that is what you have, it typically leafs out very late in the spring, about when the iris bloom. If it experiences winter damage, it might also resprout from the ground (roots). So you might want to give it some time and see what happens. I'm sorry about your plants.
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