Hi Rebecca,
Doesnt sound good, but if you still have some green, then you are correct in thinking that it is still alive! There are are few things you can do. The first being spraying the plant with HVH wake up spray. Wake up spray contains Gibberillins which induce new shoot formation, and new leaves. Sometimes when a plant is stressed and drops all its leaves, it may need some help telling it what it must do next and wake up spray does just that. The next thing that you can do is try and prune the roots of your hibiscus. It sounds like this is a pretty old plant, so root pruning may invigorate the plant and cause it to send out more top growth. Trimming the roots is the quickest thing you can do if you need to order wake up spray. Using both in conjunction will hopefully get your stressed plant to send out new leaves and eventually blooms. Hope this helps