SPY and the Vanguard version together represent half a trillion dollars of wealth under management. And that's just the top two. So yes, you can dump that much in index funds.
From other comments: Vanguard's 500 index manages ~500 billion (dmoy), Gates is worth ~100 billion (kevindqc). Even so, Vanguard can't just increase their fund by 20% like that.
Right you're sorta missing the point though. Vanguard outside of the s&p 500 has another 3.5 trillion or something. They could absorb bill gates net worth.
Vanguard's 500 index alone represents 550 billion under management. (It's split into 4+ expense ratio classes depending whether you have 0, 10k, 5m, 50m, 5b or whatever)
