Have you checked right down at ground level (just thinking it might be a bit hidden in the middle of the hedge) for new leaves? I thought mine had copped it, but it is now making a comeback.

If its regrowing at all, it will be right at the base as Weeding suggests, so check for signs of life. If nothing, then its dead and needs to be removed.

I lost my griselina, that I had for many years, there is no sign of life at the moment but I am going to give it a year befor I do anything about it, it will leave a big hole in my shrubery, so it needs thinking about