Do you really believe Google is ready to lose at least 20% of their staff? That would be a horrible decision especially in the market we are currently in. These people will easily find jobs elsewhere.
I doubt Google will lose anywhere close to 20% of its staff, and I assume Google doubts that too. I expect the rest of FAANG+ will follow suit, and there won't be that many jobs where you can earn a FAANG-level salary without being vaccinated (either because they're fully remote or otherwise). When push comes to shove I don't think that many people will be willing to take six-figure pay cuts.
Edited to add: In terms of whether Google "should" do so, I assume they've thought through the trade-off of increased attrition vs. reduced risk of COVID outbreaks (among other factors) and decided that allowing unvaccinated people to either go back to the office or work remotely would be a net negative for the company.