Anytime! I've seen a couple other developers do that, they add just enough content for you to get your feet in with the game and then send you off on your own or just outright end the demo.
I feel as though, unless you totally rework the game and change everything about it, this web version could be left as it is, a perfect if not better example of a demo. It's not incomplete, it feels fine and fluid, and if you told me the game's mechanics were complete and all you needed to do was work on areas and story, I'd believe you.
I'm actually kinda excited to see the rest of the game's development process.