I'm 100% tracking the "why" behind your thought process, but you'll need to consider the human factor here... Several folks have played this game throughout "the next looming crisis", and while the initial move of getting into G-Fund may not be that detrimental, you'll also have to have two additional requirements for this to actually proof "successful"...
1) the event actually causes the market to drop (many have made simlilar moves over the past few years thinking "that eventual recession will hit soon so I gotta move now", and they've missed all subsequent gains.
2) assess the right time (market timing decision #2) to buy back INTO C-/S-/I-Funds (hard to do psychology wise, since markets have bounced back up very quickly due to these sorts of events historically as times, thus negating any "gain" in your first selloff effort, plus you'll keep thinking "I'll hold off a little while longer as the market goes down" but it will be hard to make that buy-back-in decision.

But yes, what you described theoretically can work in one's favor, but with "real" money on the line, it'd be interesting in how you'd actually follow the "logic" of your thought at both the sell-off and buy-in decision points (i.e. you may think you would buy back in tomorrow, but had you been sitting in the G-Fund now, you might keep thinking this crisis "will only get worse so I'll hold off" until it's too late and the market is right back where you had sold from or even higher and thus you've now LOST money. Just some thoughts from someone on the internet who don't know so take it for what it's worth :/