Not exactly. At 70% (like today in much of the world) that's certainly a practical option for most people. At 10% not so much.
So what happens is that beyond a certain point it stops making commercial sense to route IPv4 globally. That's probably before your 10% mark. So by then there's no point bothering with IPv4 for your systems unless you specifically serve that deprived market and will spend money to connect to them specially.
For IPv4 users the Internet still mostly works, when their system asks "A? some.website.example" and there is no A record because the IPv4 Internet isn't really a thing any more, it gets an answer like "10.20.30.40" where that address was arbitrarily picked as a temporary local assignment for some.website.example. When they connect to 10.20.30.40 a Network Address Translation module behind the scenes does an IPv6 connection to some.website.example and hooks them up.
So their copy of Internet Explorer still "works" although some more advanced features are flaky or missing but hey, they know they have crappy 20th century Internet and ought to upgrade.
Inside some larger companies there already is no IPv4, and that will spread, inconsistently but it will spread, because IPv4 is a pain in the backside, it's easier without it. Translation gateways keep things mostly working enough for people who have IPv4 only, today that's the majority, a decade from now it's a minority, and eventually it's too few people to care about.
Eventually (probably much below 10%) the translation gateways are thinly used enough that "nobody" proactively notices if they're broken, that'll happen in some places faster than others, but the effect is to push those final people to upgrade because it's just annoying to always be the person calling your ISP to complain when it breaks.
