15 thousand to 45 thousand rounds as a rough guess.
Unless you damage it, it's dead when you decide it's not shooting tight enough groups for you.
A benchrest shooter will replace barrels much more often than most because they are worried about ultimate accuracy. A person like a friend of mine with is close range training rifle didn't even care until it started keyholing. And the baffle strike.
Most people, shooting at typical ranges, up to say 400 meters maybe, will be fine for quite some time. Is 3 MOA good enough for you? 2? 6? It's a call YOU make.