Im in zone 5 as well. I suspect that most garden shops only sell whats compatiable (or they should) to local growers. With that in mind and this is the case hopefully from the sound of yours this will winter over and come back. However becuz its new it really needs to establish itself for at least a year and thats gonna be again based on hopefully u got good healthy stock condusive to zone 5. So you may want to bank it up so to speak to give it extra freeze protection. I put up dowels in a well rounded out circle then attached some 3 ft wide bubble wrap(sold at walmart) to that..then i used a giant bag of soil poured all around the tree hisbiscus i have to bank it to at least a depth of a foot. You know our freeze depth can be at least at time 10inches. The bubble wrap i figure to help as a wind barrier against wind burn as im on a lake and it holds the dirt in place which will be easy to remove in spring and used elsewhere unlike leaves which harbor insects or pine needles which are very acidy, thats why i just used garden soil. I also,on top of the soil within the circle gave a additional frost/freeze layer of protection using are ya ready those styrofoam packing popcorn thingy's giggle..water as well as air will filter thru these and in my opinion will act as a light blanket. Gawd how we baby our hisbiscus..Good luck i cant say it will work as im only trying this myself for the first time. Trim back in SPRING.

P.S. Even if u bring it indoors dont get rattled at leaf drop from what i read and see this IS normal and it will look rather sad for awhile. Oh yeah cuz of our zone come spring DONT GIVE UP ...ITS SLOWWWW to show signs of life again usually not till late may almost june. Id take a chance and leave it winter outside. As i said sounds like you got one that will winter i have a red LORD BALTIMORE but ive seen the ones u describe around here and folks dont bring them in and they are fine. Just dont give up any plant has a really hard time for the first and second year.

garden shops will sell tropical hibiscus in places like IA, NY, and PA... of course they will die at the first frost if left outside. Without a picture dont know what you have...