What would happen to an S&P500 index if the bottom 40% of companies went bankrupt simultaneously?

What do you think would happen to an S&P500 index ETF if say 40% of the companies in it collapsed, let's say the bottom 40%?

Do you think it would just automatically sell all the companies as soon as they fall out of S&P500 status and replace with the next biggest 40% or companies? And would this absolutely tank the index's price?

I'm unsure about how this would work – does anyone know?

Thank you.