The phrase "a friend who left" is correct and usable in written English.
You can use it when referring to a friend who is no longer present or has departed from a situation or location.
Example: "I often think about a friend who left for another city and how much I miss our time together."
Alternatives: "a friend who departed" or "a friend who moved away."
So he started Neuromagic with a friend who left IBM Japan.
An artist, a teacher, a friend who left his mark on this world through his life and his works.
After travelling around India with a friend, who left to go home, she found herself alone for the first time, staying in a beach hut in Goa.
"I had a friend who left to go to London yesterday and he was afraid, afraid to go to London," said Giuliani.
I ONCE shared a kitchen with a friend who left a trail of vegetable trimmings, dirty bowls, rejected greens and uncapped vinegar and olive oil bottles across every surface whenever she made a salad.
A few years later, I passed the same copy on to my younger brother, and was incensed when he passed it on to a friend who left it on a bus.
Doug House, chairman of the Rock Island County Democratic Party, said the congressman was a dear friend who left larger-than-life footprints.
In "Hackensack" a man working for his father waits for the improbable return home of an old friend who left town and became a successful actress.
I assured an American friend, who left Jordan to study law in New York, that a new US administration will bring a sense of optimism.
Penny Monge, 45, a close family friend who left memorial candles in front of the apartment building, said that an electrical fire in Ms. Wilson's last home, in East New York, had led her to move to Bushwick.
Several months ago, a young pregnant friend, who left private law practice for the more "family-friendly" U.S. government, told me that she did not have enough sick leave to stay home for a month after she delivered her baby.
