In my opinion text adventures are ABSOLUTELY NOT outdated. Obviously, they are not the dominant genre, but there is still a relatively large and very loyal community that greatly enjoys this type of experience. In fact, there are players who are specifically looking for deep stories, meaningful decisions, and carefully crafted worlds, and that is where text games continue to shine.
The chances of someone buying one instead of playing something for free? It depends on what it offers. If the story is good, well written and promises a more polished experience than the free version, many players are willing to pay. In this type of work, the narrative is the product, and when it is solid, the value is noticeable.
I personally believe that one of the most important parts of any game is the narrative, and text-based games allow you to focus on that without distractions. They can be immersive, elegant, and emotionally powerful. For me, when a story is well written, the format not only doesn't matter... it can even enhance the experience!
Good luck with your game if you finally decide to go for it!