They're not particularly long-lived plants, Dave. Did you manage to save any of the seeds?

If you can see any new growth at all, there's a chance for it, but it's worrying that the leaves have dropped off...it could be a victim of drought. Are the stems brittle?

This happened to my tree lupin many years ago. As SH says, they are not really 'perennial' and don't last long. Even if there's a bit of new growth, they linger on rather than flourish. They are so easy from seed, just sow some more.