They do tend to die suddenly, especially after a very cold winter like this year's and some are quite short-lived anyhow.

Scratch off some bark and see if there is any green below or trim it a bit and see if there's any sign of life anywhere.

I have two of them ; the young one is fine a full of leaf and the older one has died.

It's a bit early for it to flower, hopefully it will sprout from low down. Don't give up on it just yet.