At some point in our lives there will probably be an event which does meaningfully impair likely future returns, and where reflexive BTFD therefore screws long-term investors. But that's not today.
It's kind of obvious what happens - no takers of debt, long term rate rise, Fed restart Qe as only resort. Inflation increases, Fed refuses to rise rates - inflation gets higher again - stocks have shallow dip then as it becomes obvious Fed can't raise rate s go to the moon Venezuela type
Time line is unclear. Huge immigration and cheap labour will slow inflation and delay reckoning so it maybe 10-20-30 years in the future but still you want to stay fully invested