That's not the point of a personal library.

Probably the refund does not account for inflation, though.

500 dollars today may not have the same purchase power of 500 dollars a few years ago.

I buy physical copies. In the cases where I buy digital media, I strip the DRM. I also support DRM-free vendors, like gog.com.

You can't depend on companies to honor their agreements in perpetuity, especially when there's no direct, ongoing economic incentive to do so.

Well having your book collection suddenly deleted is not convenient either...

So, the alternatives: 1. Buying a real/paper book 2. Pirating/illegal downloading

The best option seems doing both, you support the author by buying the real book, and download a pirated copy for convenience.

DRM-free eBooks aren't actually all that hard to find, though it varies by publisher. There are plenty of publishers who sell all of their books DRM-free. And plenty of larger platforms like Kobo tell you at the bottom whether it's a DRM-free EPUB or has Adobe DRM attached, etc.