They'll be (if the exist) the exception rather than the rule. Fans will fail long before 8 years of 24/7 use. Loooooooong before.Any issues on thay card wont be down to mining on it for 9 weeks, there are cards still running from the first mining craze back in 2010/2014
Many miners plan to replace cards running 24/7 after 3 years or so.