^But that's just it -- after a while, once the show has established its own identity and direction, it wouldn't be trying
to follow the same storyline as the novels anymore. It would be constructing its own version of the universe that might draw on elements from the novels but would put them together in its own distinctive way. It's just natural that over time, the two versions of the work would diverge more and more as the differences increased.
To offer sort of an inverted example, consider The Hitchhiker's Guide to the Galaxy
. This started out as a radio serial and then a couple of record albums before it became a series of books. The first book was pretty much a straight adaptation of the first few episodes of the radio series, albeit with an altered ending so that a cliffhanger moment in the radio show had a more conclusive resolution in the book. That meant the second book had to shuffle things around, still incorporating a lot from the radio series but putting it together differently, leaving out some bits, and adding other bits. It ended in much the same place that the first "season" of the radio series ended, though. But then the third book ended up going in a whole different direction from the radio series, with only a few points of commonality (in fact, I think it was largely based on an unused Doctor Who
pitch), and later books just diverged more and more radically, so that most of the material in the second "season" of the radio series never got adapted into prose (or indeed any other format as far as I can recall).