If the root ball dried out, you may have to dig them up and soak the root ball to get it wet. Once the root ball dries out, it is very difficult to get it to take water. Just soak until it gets heavy. All this talk about watering shouldn't let us forget that azaleas also need good drainage, not standing water. Here is a link that might be useful: How to care for rhododendrons and azaleas.

If it's powdery mildew, you should be able to scrape off at least some of the white. But perhaps it's azalea lacebugs. In this case, the very small critters -- if they're still present -- will be on the back sides of the leaves. You should also see small dark specks which is -- umm -- the critters' excrement. And if it is lacebugs, it's very likely you won't find live insects at this time of year. Typically they're present earlier in the season. Relatively few folks notice the damage while it is occurring.

If I understand that you typically keep this plant inside next to your window, but left it outside while you were gone....that's what happened to it. Add whatever the water situation was on top of that. Your azalea (the next one) should be kept outside at all times, in an area protected from the full sun. Mine, which are probably more mature than yours, get watered every day except in the winter or if the weather is very dark and rainy (which hasn't happened this summer/fall). I do bring it them in to an unheated but protected location in the event of a severe freeze (20o). This azalea might not be a goner yet, only time will tell that for certain. But I would certainly give it a fighting chance by keeping it outside where its chances of coming back in the spring are much greater. Azaleas are rather difficult to grow inside...they don't the location much, lol.

It's too early to give up on these azaleas. Both show the classic signs of winter burn, damage from a combination of cold, sun and wind. Z5 is very difficult for most evergreen azaleas so some form of winter protection such as burlap screens or evergreen boughs is advisable. The deep snow of the 2014/2015 winter provided excellent protection. This was not the case in 2015/2016. It is also quite likely that the azaleas entered the winter in a dry state because of the root competition from the Norway (not Northern) maple. Growing anything within the root zone of Norway maples is difficult but not impossible. Rhododendrons and azaleas can actually do pretty well because of their dense fibrous root systems as long as they are given extra water during dry spells. Don't try to remove the maple roots. Cutting them just stimulates more vigorous growth. Instead, plant on top of the ground in a coarse planting medium of mostly conifer bark. In any case, wait until more settled warm weather before assuming your plants are dead. They may be, but there's a pretty good chance you will begin to see new green buds along the stems once things warm up. You might also think about getting rid of the maple. Professional tree removal is expensive, but Norway maples are incredibly invasive and are in no way a desirable tree. A whole new world of gardening would open up for you without its dominating presence.