The unsatisfying answer is that there is no real way of knowing without closer examination.
You are quite correct in your observation; these trees are distressed. Most trees like to be above the water table, although there are species that can stand in water for an extended period with no discernible ill effect. These trees are exhibiting typical symptoms under stressful conditions, shutting down until the danger is passed. If they have survived, you may see them starting to put out buds and leaves again, although this will force the trees to use some of their reserves which may weaken them somewhat. You may even see them flower again as a survival mechanism.*
One way that you can get an idea as to their condition is to scrape a bit of bark off one of the twigs or branches; don’t do it to the trunk. If you can see green, the tree is not dead. Yet. But don’t write them off until next year. I’ve seen trees completely denuded by gypsy moth caterpillars, and they only came back stronger and fuller the next year.
*I bought a Davidia in the spring six years ago; this tree is known for not producing flowers for up to the first ten years of its life. I went away for vacation that summer, and like an idiot I forgot to water my tree before I left. I came back to find that it had dropped all its leaves. I watered it like a maniac, and the leaves eventually came back. Along with three flowers that never appeared again until this past spring.