Answer: Based on your description, it sounds like there has been a problem at the trunk (possibly injury such as by a weed whacker or a rabbit chewing) and the bark has died and begun to decay and the wood has begun to deteriorate as well. When a trunk is severely damaged, the top of the plant consequently dies sooner or later and it sounds like this is what has happened to your shrub. I would not expect the top to grow any more and in fact would cut it off below the trunk damage.
It is possible, since this is a very resiliant plant, that it will resprout from the base and regrow -- unless the damage is so severe that it is well and truly dead. Plants regrowing from an established root system generally regain their size very quickly. Since rose of sharon blooms on new wood of the season, if it does regrow it should also bloom for you this summer.
At that point, it is a judgement call whether or not you want to wait and see, or if you want to just replace it now while the season is still amenable to planting a replacement. I'm sorry about your shrub.
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