What gives you any reason to doubt that they will?
Things don't enter the public domain anymore, sorry.
I'd actually be pretty happy to pay a small subscription to websites that I use all the time, and that seem to be worth it. Of course, there are a lot of websites that would die very quickly without advertising, and I don't object to that at all. They can go, and that is fine.
I think a reasonable subscription to a website I really like would be something like a $1 to $1.50 a month. If enough people are paying, that can easily cover the costs.
Of course I'd rather have those websites supported by voluntary donations. Lets not pretend that it doesn't work, just because Wikipedia are hopelessly greedy and over-ambitious. For many websites it can work fine. I know at least one for which it has worked for more than a decade.