If there's absolutely no sign of life by now, not even at the base, near the ground, then its possible its died. Snap off some stems - if they snap off easily, they're dead. If you're not sure, peel back a bit of bark with a fingernail - if its bone dry and brown, its dead, if its moist underneath, its not.

My neighbour thought hers was dead and cut it down to about a foot from the base and now its just beginning to sprout new growth so perhaps there is some hope for yours.

Thanks for your advice, I'll have a go and see what happens.