>The only way to keep the things you buy is to actually own them. Not continually rent them from one online service after another.
Eh, as someone who has owned (and lost or destroyed) a bunch of physical things, my experience is that I have to continually rebuy physical things I use; I mean, records, CDs, books... these all get lost and destroyed in various ways if you carry them around with you and otherwise use them. I don't think that the way I own and store things is more reliable than a major content licensing platform. If I use a thing consistently and long term, then licensing it is certainly more reliable than buying a physical copy, and may very well be cheaper for me than buying physical copies new.
I'd argue that what protects availability of things that go out of print is more that other people own the thing and can sell me a copy when mine is lost or destroyed. You could argue this is a bit of a tragedy of the commons, or it could be, if E-books started pushing physical books out of print (as opposed to books that are e-only mostly being books that wouldn't have been printed at all before the advent of e-book technology)
Of course, for things that are rare (and things that are popular are a lot less likely to go out of print) this gets expensive pretty fast, but first sale doctrine does assure me that I can usually get a copy, if I'm willing to pay enough, while the possibility does exist, with electronic copies, that I won't be able to get a copy at all... that's true.