James, any answers to the questions jeffrycope and I posted?
The hedges should normally be able to survive for many more years as I have some that were planted in the 1970s and are now huge. But it is important to know if you noticed symptoms of problems or weather issues.
For example, I can research your weather if you send me a city/country or a nearby large city name. I do not need an address of course; just a city/state/country) to know if you are in a cold region, southern/warm areas of the US; southern hemisphere, etc. I am in the United States, near the Dallas area of Texas.
For weather-related issues: In the tropics and parts of Australia, you would get one answer. In semi frost free areas like Florida, you get another answer. In colder locations, you get another answer.
For other issues: It also helps to know if there were unusual symptoms before the problem started to see if there pests involved or fungal issues.