If “a couple of years” means you might not have to start withdrawing in 2+ years, then historically that leaves time for things to have bottomed out by then.
If that holds true this time around as well, then making automatic contributions of a fix amount, means that you’re currently investing at low prices, which buys you more shares. And, making extra contributions further amplifies the effect.
So even a modest recovery by then can generate good growth.
(While everyone likes the vibe of a booming market, it’s actually the hardest time to invest successfully.)
The biggest problem is for folks who are forced to withdraw in less than 2 years. If they don’t have other funds available to them to hold off selling 529 investments, they might have to realize some losses.
Of course, all is relative:
My 529 account is >20 years old. I will probably be selling one of the funds at 10% less than what it was at its peak, but then again, it just means my profits in that fund are “down” to +38% from +48%.