Does the yeast in a starter die off once the starter is established?
Am guessing the yeast just joins its fellow yeasts, which develop through the flour and water.
The first starter I ever made was Alton Brown's Proto-Dough. It includes yeast and in retrospect, quite a bit of flour. I foolishly mixed it in a quart jar and several hours later, was horrified to see it growing out of the jar. The Blob had arrived!
I moved it to a gallon jar and kept it going for several months. It was probably the best tasting starter I've made, once it had aged. It was tossed by mistake at its prime and I'm contemplating mixing another batch.
Not unless the starter is abused or neglected, the purpose of a starter is to grow yeast & lactobacillus. I assume you mean commercial yeast, which like wild yeast will not die off if fed at regular intervals.
If you are talking about a sourdough yeast, commercial bakers yeast can not survive in that environment.
In fact, it isn't a sourdough starter until any commercial bakers yeast has died off. If you are a sourdough purist, you'll avoid the use of commercial bakers yeast, cabbage leaves, grape leaves, grapes, yogurt, buttermilk and citrus and other food juices when starting sourdough starters. They aren't needed and are counterproductive.
They add yeasts that can't survive in a starter, bacteria that is the wrong sort, food that the culture doesn't need, or acidity that will at best speed the startup by a day or two.
...that the commercial yeast in a starter died off, or joined its so-called natural yeasts as they developed in a starter. Matter of fact, I probably read it here! A lot has been talked about and written about the "pure" starters vs the ones that begin with a little "commercial" yeast in them, so I wondered if, once a starter became viable, what happened to the bit of yeast I added at the beginning of the process. My starter is now one of the healthiest I've ever had, or seen.