Root rot normally kills the entire plant rather quickly. Drought and dieback will kill individual branches as will borers. Prolonged drought weakens plants and often results in the appearance of fungal cankers on the branches of older azaleas. Look for branches that wilt in hot, dry weather in late summer and be sure to water azaleas if drought drags on more than a few weeks. Prune out the affected branches to stop the spread of fungal canker diseases.

There is another possibility: The roots of Black Walnut (Juglans nigra L.) and Butternut (Juglans cinerea L.) produce a substance known as juglone (5-hydroxy-alphanapthaquinone). Persian (English or Carpathian) walnut trees are sometimes grafted onto black walnut rootstocks. Many plants such as tomato, potato, blackberry, blueberry, azalea, mountain laurel, rhododendron, red pine and apple may be injured or killed within one to two months of growth within the root zone of these trees. The toxic zone from a mature tree occurs on average in a 50 to 60 foot radius from the trunk, but can be up to 80 feet. The area affected extends outward each year as a tree enlarges.

In any case you should be able to replant. But first make sure there are no black walnut or butternut roots in the area. If so, clear them out of the bed and put in a barrier to surface roots. Also, figure out why this bed is more prone to drought damage. You may need to amend the soil with bark compost and use an excellent mulch after planting. If the sun is hitting the side of the raised bed, then that could contribute to the drought damage. You may have to put in a layer of insulation along the south side.

After planting be sensitive to needs of the plants. When dry, azalea leaves will droop in the morning. If they droop in the heat of the day, that is normal and not a problem. But if they droop in the morning, then the plant needs to be watered. Don't overwater and make sure you have good drainage. Wet roots is the main killer of azaleas.

Here is a link that might be useful: How to care for azaleas

Thank you very much for the detail answer.

when you say 'You may have to put in a layer of insulation along the south side' what do u mean? :-) sorry, I do not know much about gardening as you can see.