Is kidney failure permanent?

Not always. Chronic kidney failure is generally irreversible whereas acute renal failure can sometimes be adequately treated and reversed, e.g., hemolytic-uremic syndrome.
Not necessarily. A person may have acute kidney failure in the setting of an injury, dehydration, heart failure, reaction to certain medications, etc. And they may go on to do just fine. Talk to the doctor about the specific situation that worries you. LGromkoMD.
Sometimes. Sometimes kidneys may fail suddenly but be able to recover over weeks to months. With diseases like diabetes or high blood pressure, kidneys lose function slowly over time. This orm of kidney failure tends to be permanent. Your doctor can give the est answer about your type of kidney damage.