I've suffered through two >50% drops in my portfolio in my life: 2001 and 2008.
The only difference is back then I was working, I don't have a job now, so the future is less certain.
If I could take any lesson I've learned from my two brushes with financial calamity, it would be, "Don't panic-sell on the way down". Ride it out. It'll come back. Eventually.
Here's a stat.
# of times in the entire history of the stock market that it has completely failed to recover: 0
How long it will take is a different matter and depending on your investing timeline and when you need the money, it might be prudent to chip away some sort of emergency fund from that hypothetical $650K right now.
Just my random thoughts...