I think it is safe. It invests mostly in US gov't debt, which is considered the safest investment in the world. If the US gov't defaulted, it would be a disaster for the whole banking system. That hasn't ever happened, going back to the when the government was founded.
A third of it is in repurchase agreements, which became illiquid during the 08-09 financial crisis. MMFs like this one were in danger of "breaking the buck," falling in price to some value less than $1 a share. To prevent people from withdrawing their money, worsening the crisis, the government stepped in and insured these funds similar to FDIC-insured bank accounts. The yields dropped to be the same as FDIC-insured bank accounts. I am not sure if they would do that in a similar crisis in the future. So FDIC-insured bank accounts are slightly safer, but they're both very safe.
If you're really trying to protect yourself against catastrophe, which I think is much less likely than the risk a healthy person dies of a sudden health problem or an accident, you could keep some gold or silver coins. They have stayed at the same value since antiquity, at least to the extent you can compare modern goods and services to ancient ones.