When we took down a couple of conifers in the garden earlier this year, we discovered a hibiscus that had been growing horizontally in search of light. We tied it up (it looks like a right mess) and had great flowers this summer. But it clearly didn't get any formative pruning - it is a single woody stem about 2 inches wide and then a tortured frame with nothing looking like new growth.
I suspect that pruning it will probably kill it but if I were to have a go, what time of year and how hard would you go ? I've no experience with hibiscuses but I took a similarly mistreated mock orange tree down to the floor in the summer and it came back. Can I be lucky twice ?