The siren call of a dying open podcast culture is the same siren call of the dying blog. Open podcasts are not dying because Joe Rogan signed a contract with Spotify. Open podcasts are not dying just like open websites are not dying.

Will some players like Spotify entice popular podcasts to be exclusive to their platform?
Yes. No question.
Does that mean that indie and small publishers will lose users?
Yes. No question.

Much like text editors, there will be alternatives to Word, Pages, Notepad, and other built in system applications.

Remember the tale of the boy who cried wolf.
If the indie web keeps saying X will be the death of the open Y, when it finally does happen no one will have listened.