If you think it will freeze take cuttings and pot them up. Only bring the cuttings inside if you expect a cold night they can be outside during our average warm winter days. If they are well mulches-protected they will still come back next spring. I keep trying to locate hardier hibiscus that will not need protection during our winter months. I grow Confederate Rose Hibiscus; a 10 foot plus tree when I can cut to the ground each year and still have a 6 to 8 foot tree by the time it blooms in the fall. I also enjoy our Texas Star Hibiscus but only have the red ones at this time. They die all the way back before it gets cold here and come back in the spring. They can get quite tall and leggy but I love their blooms. Of course they also can be pruned to keep them within the limits you want.
Always talk to your local extension agent.

I am in zone 8b and I cut them down to the ground and then cover with pine straw. As soon as it starts warming up for the year I uncover them. They normally won't bloom until it gets good into the summer but they do survive here (south west Georgia). I have started to over winter more and more tropical ones, so many that I am digging up and getting rid of my so called hardy hibiscus because I am constantly fighting bugs with them and I don't have that problem with the tropical ones.