Give it lots and lots of water every day to see if this helps. It may take a while to recover enough for you to see new growth, if it is going to recover, that is.

I agree and also I would be tempted to reduce it in size and give it a light trim, at least cutting off the dead bits.

If its suffering, reduce the topgrowth by at least a third to lessen the stress on the roots - water frequently and plentifully until autumn/winter.

Whack it right back to about a foot, Dont panic it will just look like a thick twig, Feed it and water it and wait.