1) Book sales have been consistently declining overall, in all media. It's not clear that DRM has much to do with this.
2) They'll still be selling DRM-free through at least one merchant, Google Play. (It's not clear whether this policy extends to Amazon as well, but they wouldn't be the first publisher selling DRM-free there; Tor's science fiction novels have been DRM-free through all merchants for a few years now.)
Source: https://www.linkedin.com/pulse/oreilly-mission-spreading-kno...