FWIW (and truth be told, its not much) my take goes like this:
The making of photography film is a very mature, very well understood process. The only real risk to ongoing availability (meaning into the indefinite future) would come from a lack of availability of some of the precursor components. As long as those components (I'm thinking about the various industrial chemicals/emulsions/whatevers that go into coating the film) are available, film will be available.
How ever small the market becomes, there will be manufacturers who want to serve it. It may very well be that film turns into more of a "craft" industry, with small shops making product in small batches.
And I can see availability getting squeezed from the bottom up in terms of format because of packaging: 35mm is harder than 120 is harder than sheet. Maybe sheet film, produced by craft shops in small batches is what the future of film looks like.
But as long as you can buy the substrate and the precursor chemistry at reasonable prices, there will always be film.