You said you had it several years. Some of the newer hybrids only live about 5 years.
Hibiscus love to be pruned and often respond well to a good pruning. Your plant is already defoliated it might respond to pruning a good 1/3 to 1/2 of it off. When we prune ours we often time prune a good 80%. Sometimes our goats have gotten into the yard and eaten them down nearly to the ground and they have always bounced right back.
Tropical Hibiscus Q&A