We know that for the latter half of Animorphs, KA had ghost writers take care of the manuscripts while she provided the outlines. She continued steering the storyline of the series, and she still wrote a handful of the books herself. Eventually she chose to let her contract expire and she created the final arc.
But what would have happened if somewhere in the 30s/40s she had walked away completely, let Scholastic make all decisions about the contract, and passed the story off to other writers, without providing them outlines? How many books would be written? What would the ending be like? Would the books eventually end abruptly with no ending, like a cancelled TV show? How would the series degenerate, or would it have been improved? Would you have stuck with it?
I think the books would have continued on for a while like they did from 36 to 44, where the series was often spinning its wheels. The main plot would rarely be progressed, and the tone of the books would dry up, losing the darkness, complexity and humor. We'd get a bunch of simplified, stand alone, bubble-gum adventures. I was really worried that that's what Animorphs was going to turn into when I was reading about Atlantis, Austrailia, the Magic School Bus, and the Buffa-human. Recycled plots, loss of nuance in the characterization, villains that seem to die but always make a comeback, jump-the-shark moments. I was worried that the series was fated to be unimaginatively milked until interest dried up, at which point the books would end abruptly with no resolution. I think I would have eventually stopped reading, if that had happened.