It is unlikely that a 50% drop in NVidia wouldn't be paired with a significant drop in the valuation of every other company heavily invested in AI.
Of course, but the top ten that make up >30% of the market don't just sell AI. If all of those lost 50% it would be a 15% drop in the index, painful but not jumping-off-building bad
Unless they too were somehow tied into Nvidia.
This is what caused the 08' crash. Everything was all tied together so as one massive bank failed it sent a cascading ripple effect through the entire industry which became a sort of black hole that took down many seemingly stable, profitable banks with it.
I can easily see the same happening with AI.