The next step will naturally be a major increase in the prevalence and sophistication of anti-adblocking techniques. We're already starting to see the first stages of this on some of the more brazen sites, but reputable companies still tend to value user goodwill more than they value the lost revenue from ad blocking, at least for now. If adblocking ever starts to become an existential threat to medium to large sized businesses though, that situation is going to change real quick. A ton of money is going to start being thrown at countering the threat of ad blocking.

The companies which do the best job of preventing ad blocking while minimizing disruption to users will survive. Those which ignore the problem and allow ad blocking or those which are too aggressive and annoy users with their countermeasures will die. Companies which don't rely on ad revenue will stand to gain. The extent of this gain will depend on how far the war escalates and how much worse of a user experience ad-supported sites become as a result.

The resulting war will slowly escalate, with ad-supported sites becoming a bigger and bigger pain to use until one of several things happens. Either:

A. Enough sites are successful in forcing users to disable their ad blockers that running an ad blocker becomes a bigger pain than it's worth, and as a result adblocking usage declines enough that the old status quo is restored (except that running an adblocker will be a much bigger pain than before for those who choose to continue using one).

B. Governments pass laws restricting the use of ad blockers, and those laws are sufficiently effective to reduce ad blocking usage to a level where the old status quo is restored (except running an ad blocker will be more difficult and/or legally dubious than before).

C. Governments pass laws banning the use of anti-ad-blocking technology. Millions of ad supported companies which are affected by these laws go out of business. (See other comments in this thread for assessments of how that might turn out.) Sites which are unaffected by the laws (or which can get away with breaking them) continue the war. Repeat.

D. Anti-ad-blocking tech reaches a level of sophistication where companies start deploying full-fledged DRM to protect their content from users who use ad blockers. Circumventing DRM is illegal under existing law. See option B for the result.

E. Ad-blocking tech becomes so sophisticated that any and all technically viable countermeasures are either so expensive to develop or so annoying to users (even users who don't use adblockers) that most ad supported businesses are no longer economically viable. See other answers in this thread for the result.