Sorry to hear about that, moonbelly. The Potomac Valley Chapter of the American Rhododendron Society, which covers DC, recommends that you avoid planting "most" of them in a south, southwest or west exposure. So if your plants were to be alive consider transplanting them to an east-facing location where they can get morning sun/afternoon shade or dappled sun.

It is likely that they may have had soil moisture problems when the summer months started so try to determine if this is the case by testing the soil with a finger inserted to a depth of 4". If it feels dry, you may want to research why and take appropriate corrective action. The finger test method should aid you quite a bit in the future. Use it daily for 1-2 weeks and make a note on a wall calendar every time that you water the shrubs. After two weeks, determine how often you water (say, every 2/3/4/5/etc days) and set the sprinkler to water 1g of water on the same frequency. Then recheck with the finger method if you notice that the temperatures fluctuate 10-15 degrees and stay there.

Rhodies and azaleas prefer moist soil. It is ok to wait until the soil feels almost dry to dry before watering but, if you wait to water too long, the plant will be stressed and will dry out. It sounds like this may have been the case.

If you transplant the shrubs or if you get new ones, try to select an area where the sprinkler system or drip irrigation can take care of this. About 1g of water per watering should suffice as long as you also maintain 3-4" of acidic mulch.

If the plants currently do not show any green foliage, things are more difficult to predict and correct. They probably have dried out if there is no green. To tell if the plant is dead for sure, you can try to prune the stems in 1" or 2" increments until you either hit the bottom or see "green". Or, of course, you can simply pull the plants out and take them back to the nursery (do they offer a refund of some kind?).

If the plants show some green then you will have to show them some TLC to see if they recover. Maintaining the soil moist with plenty of mulch & applying no fertilizers would be the things I would do in that case. I would prune out the dead stuff in the Fall or after the plants leaf out in Spring.

If there is no green or if you do not have time to monitor the soil moisture often this summer, I would replace them provided the nursery will do it.

Good luck,
Luis

Here is a link that might be useful: Potomac Valley Chapter of the ARS