It also matters how much they weight it.

> So even though SpaceX would be a $1.75 trillion company, many index funds that include it would have to treat it like a $70 billion company. In Vanguard's total-market ETF, then, SPCX would enjoy a similar weight as $73 billion retailer Ross Stores (ROST) — currently the 157th-largest stock in VTI, accounting for about 0.1% of its assets.

https://www.kiplinger.com/investing/index-funds-and-mega-cap...

So someone with $10,000 of VTI might have $10 of SPCX. Not a big loss for them even if it went to zero, and the whole point of that index is to have some of everything.

(QQQ is a different story.)