If you're talking about Salix hakuro nishiki (rather than Acer negundo 'Flamingo') then the time to clip it to shape is spring, not autumn. Doing it in autumn can force new growth, which gets killed in cold weather, and can cause dieback.

And in Spring means just after the catkins (if it gets any) have finished. That is if you want catkins.

I fear if it has had no leaves all summer you can think the worst, but perhaps give it until next Spring just to be on the safe side. Scrape the bark with a fingernail and if the underneath is green you have hope. If the wood is brown it has no life in it. Willow is a very determined plant and it may just send up a shoot from the base if that's what it is..