If you'd been DCAing a fixed amount monthly into stocks for 10 years prior to the 2007 peak, then during the crash continued doing so without selling, the total value of your portfolio would've matched its pre-cash peak in just 3 years and exceeded it significantly by the time the market itself recovered in ~5.5 years.

3 years is really not a long time. So I'd say it comes down to emotional fortitude and probability of staying employed. If your time horizon is longer than 3 years, the calculation of whether to sell should essentially come down to calculating your odds of keeping your job. I bet it's possible to build a robust mathematical model that recommends a decision given your best personal estimate of your layoff probability during a severe market crash.