I'm more concerned about content I create, which is where I depend much more on tools. I put a LOT of time building my world RealmWorks, which was at least installed software, so I still have access to it, even though it is no longer developed and barely supported by Lone Wolf Development. With database tools like that migrating content is a pain, so I am shy about putting too much of my stuff in systems like that. I like World Anvil, for example, but I worry even more about content lock in.
When it comes to purchasing content, it depends. I'm more worried about my Kindle books than D&D Beyond. I really don't like the idea that I can buy a book and have access to it removed or have content changed via legal actions, etc. For literature and reference materials, my Kindle library has replaced my physical library. I only keep physical books if they are display worthy, have nolstalgic value, or are the kind of reference book that is more convenient to have in a physical format.
For D&D I buy many of the books in physical format because I enjoy paging through them and just like having a bookshelf of the books. But I don't buy every 5e book. I also have a D&D Beyond subscription. I don't mind if that content changes because I see it as just the current, constantly updated system rules and adventure content. While it is double paying in a sense, I still find it worth it because I can link D&D Beyond to my VTT without paying an additional cost. The D&D website and offline app are all well designed and is what I rely on in game and most of the time when prepping games. I would be nice to have PDFs of the D&D books just for archiving, but I would still prefer to use D&D Beyond over PDFs.
If D&D Beyond were to disappear that would be annoying, but I have physical copies of the most important books to me and finding used copies of books I don't have should be easy to acquire for a long time to come.