There are a few problems I see which will combine to make film use harder and less popular:
1. the cameras are getting older and almost nobody is making new ones. There may be plenty around on the 2nd hand market for a while but their supply isn't likely to improve much, and certainly not in the long term. The number of people skilled in fixing them will dwindle too.
2. film availability, but as has been said, it's likely that there will be enough niche operators around to keep that going - I don't think that will be a deciding factor, but it won't be available in the supermarket and will stop casual users.
3. processing labs: again they will dwindle as it becomes harder to justify commercially but it will take a LONG time before there's nowhere out there to get films developed. And even then, enthusiasts will be able to do it themselves. It will stop a lot of us who can't be bothered though.
The internet is a great preserver of niches - and film photography will benefit from it too: you can buy everything you need for film photography without getting up from your PC, and can find plenty of enthusiasts to discuss it with too!
Overall, I can't see it stopping anytime in the next 20 years, though it is likely that before that most small and medium format film cameras will lose most of any advantage they still have over digital. Personally, I still love the look of film and even if digital can match that some day I'm not sure I like the idea of a format that is just trying to replicate something which already exists. I also love film cameras and get little joy out of using dSLRs.
Beyond 2030, who knows, but people will still love and cherish their Leicas, Nikons, Hasselblads, Canons (and Holgas for that matter), and there will be enough wanting to still use them to keep a trickle of availability going I'm sure. We will see...