NVidia makes up 7.5% of the SP500. If it lost 50%, it would be a 3% loss for the index. The concentration is bad, but it would not cause a drop of 50% retirement funds by itself. If you take an all world index, it's even less.
Still, if NVidia lost 50% of their market share, we would probably see a big collapse of the stock market.
EDIT: to note, the top ten companies in SP500 make up an unprecedented concentration but they're not "mostly AI".
Still, if NVidia lost 50% of their market share, we would probably see a big collapse of the stock market.
EDIT: to note, the top ten companies in SP500 make up an unprecedented concentration but they're not "mostly AI".