Yellow leaves on hebe

I made an ill-conceived "mixed hedge" with hebe, escallonia Apple Blossom and buxus out the back a couple of years ago (the hebe has dwarfed the others and now I have time to get round to this part of the garden I realise this area gets too much lovely morning sun to waste on a hedge!). Going to ditch the hedge but I'd like to keep the hebe. Unfortunately, it has a lot of yellow leaves. Is this water stress from the drought or something else? How  can I help it? And do I strip the yellow leaves off or not?
Thank you.