In regards to the hypothetical Y2K retiree with 100% stocks allocation. Assuming this is an absolute diehard who rides and dies with 4% and 100% stocks no matter what, which would be absolutely incredible given the circumstances. Lets assume they were 30 when they retired. Today, they are 52, with $512K in assets. At this time, they decide its time to make changes. They continue pulling 4%, or roughly $1,700 per month.
Assuming again, this person had a $40,000 budget, with inflation that is... about $67,000. Or, $5,500 a month. So, this person would be staring at a $3,800 a month deficit in spending. Given current wages, that is certainly doable(basically a salary around $60K a year), even for a 52 year old who has not worked in the last 20 years. However, even if it was not, a combination of a new job, and some cuts to spending could probably sustain this historically unlucky person the next 13 years to age 65, when they could collect SS, and combined with a more aggressive drawdown of their portfolio, could sustain them until death(which would be somewhere between 10 to 15 years).
This is the not the absolute worst case possible(that would be major health problem, lawsuit drains your money, children are kidnapped and ransomed draining your account, etc, etc, etc...), but it is pretty close. And this scenario has a lot of improbable assumptions. Like that this poor soul rented their whole life, instead of buying a home, which would both blunt the costs of inflation and provide some emergency cash if needed.