When “K” is in the process of texting someone and he’s typing but he doesn’t submit it and he doesn’t delete it either, he just leaves it hanging as a draft as he goes on with his day, will the other person keep seeing these undulating “K is typing” dots forever? Or will the dots disappear if K doesn’t submit the text?

That depends entirely on the specific application you are using, but I can’t remember ever coming across a messenger that did not disappear the dots if nothing has been typed in the past several moments.
Thank you