We had a horrible drought last year in TX, which they said was the worst on record in 100 years. I had to turn my back on my flowerbeds and let it go. Water was scarce and it was not even effective to water the beds because it evaporated before it could soak in. This spring, I was srprised to see the things that actually DID live. Seedlings for many perennials popped up everywhere! The mother plant may have died but there were many offspring left to be transplanted. Almost all of my established plants (irises, bulbs, clematis, daylilies) lived. I did lose a few roses. The plants that survived rooted deeper and they bloomed better than ever this spring.
Sometimes the top growth will die but the roots are still alive and then they might come back next year, but some of them may have actually died. Hard to tell though until you wait until next year and see what comes back. And as MiniPonyFarmer mentioned, if the plants did bloom and go to seed earlier in the year then you could still get some reseeding so you may "save" some things that way too.
I would say if the plants were ones that you just planted this year then your chances that they are still alive are lower because they wouldn't have had time to get their roots well established. But if they're things that have been in the ground several years and were well established then there's a decent chance some of them will come back.