If you live in the north you probably wouldn't know until next spring. Even though some plants look dead they just might have gone into dormant mode.

Established plants with deep root systems will be fine. Last time, the only thing I lost was some lawn grass. I didn't have hydrangeas then, but had a lot of roses and perennials.

I can't speak to other parts of the country but perhaps my local experience can help.

Because of our rainfall patterns, the PNW is a recurring summer drought area. We receive very little rain between the beginning of July and the end of September, typically an inch or less each of those months, sometimes much less!

Native plants by and large are adapted to this pattern although they often show signs of drought stress by early fall. But unless designed specifically for drought tolerance - and many are - cultivated gardens require regular irrigation. Lots of landscapes would not survive without it! The exception are lawns. Many homeowners will allow their lawns to go dormant by withholding irrigation, knowing they will come back to vibrant green life with fall rains.

Although not unheard of, water restrictions are not common so everyone waters as needed, even though summer water usage bills can be huge due to a seasonal surcharge, depending where exactly one is located.

To answer your question a bit more directly, plants in the garden or landscape that are not used to extended periods without water, either rainfall or irrigation, can be stressed beyond recovery, sometimes showing that evidence almost immediately and sometimes not evident until the following growing season.

A week without measurable rain here in summer means watering or irrigation must be supplied. I should think that would be similar for you as well.

So we have two very different views from gsllica snd gal. I am in New York like gallica so I hope her experience will be mine. I also wonder if gal’s standards are higher as a professional. I am looking for survival only at this point!