I would dig them up and put them into pots, where you may be able to nurse them back to health, with a bit of judicious pruning. What form is the dying taking, rotting stems, falling or wilting leaves?
It may be vine weavils eating away at the roots, so when you dig them up have a close look at what is going on at the base.
It's been a really hot, dry summer in a lot of places - very challenging for new plants to get enough water in these conditions because it takes them a while to get established in the soil. Generally, it's easier to plant shrubs in spring or autumn, when water isn't such an issue.
Florentina's advice of establishing a plant hospital where you can nurture them back to health is a good plan!
Sorry, meant to come back with answers. Have just realised, we had the grass treated a few weeks ago, by someone who is going to come 3 times a year. Could that have killed them all? He said the plants would be okay, but even my well established Lavatera and Buddleia bushes are turning yellow from the bottom!