Is there any chance that supernatural will be back on Netflix or will it be gone forever?
Probably nobody here knows that. But you could suggest one or more titles on Netflix on the help page…
You don't know. Since the series is over, that probably won't happen. I'm watching the series myself on Amazon right now and hope it stays there until I finish it. Otherwise I have to buy the series on Bueray or DVD.
That's the big disadvantage of streaming. As in the cinema or on TV, you can only watch films and series as long as streaming rights apply. Even if you buy them to stream.
I also watched the series on Prime. I just asked about a friend