Certified GKH Gardening Expert
There are many things that can cause hibiscus leaf drop. This article can help you with what might have caused yours: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/answers-to-what-causes-hibiscus-leaves-turning-yellow.htm
While the article is focused on yellow leaves, the reason for leaf drop is normally the same as what causes the leaves to turn yellow right before the leaves fall off. Most of the time, the hibiscus recovers just fine and the leaves will normally regrow.