Yes...I thought of that.
But...wouldn't a prudent world (yes, I know, we ain't good at prudence) keep a good kernel of such animals in case something went wrong with the lab meat production?
One would hope so. But it would be hard to reproduce enough herd animals fast enough to feed the world if the artificial production were to fail suddenly (not sure why that would happen though).
But my point had more to do with simply observing that many species/breeds of animals that exist today do so only because they are food sources for us. Any attempt to replace them as food sources really doesn't do much good for the animal populations themselves because they will quickly vanish. Unless you argue that it's better to not exist at all rather than existing as a food source.
I guess it depends on why we would want to produce artificial meat. If it's for a new flavor, or for a redundant source of meat, then I guess we have little to lose (and may even gain as a result of redundancy and variety of sources). But if we're trying to do it to be kind to the existing herds, then it may not have the effect we expect.