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.

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.

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.