Major websites are ad-funded, the internet isn't. Networking technology, IPV4/6, http, ssl and most website frameworks aren't funded by advertising ( and even if they are eg react, they won't disappear.)

Let FAANGs fail. Let them try to disguise ads into content, fail and go off the deep end. What is there to lose, really? Search? Someone will take their place. Instant gratification online ordering (not funded by ads but fuck it) orchestrating modern slavery? We'l be fine. Facebook products? Might be a bit of a panic as chat for 50% of the world population goes down, but we'll manage. RCS is good now, matrix is right there, we'll manage. TikTok? We'l be fine.

Pretty much any thing funded by advertising is not vital to society (otherwise they could make you pay for it) and like half of it is parasitic.