If SpaceX joins and goes to zero, that is firstly a 2 Trillion dollar wipeout and the whole market would absolutely go completely crazy and the market would be so spooked as @etempleton suggests that instead of it being a 5% drop, it would be more like 50% (don't quote me on it) but still, the markets would absolutely drop substantially more than 5% & it might erode the trust within financial markets altogether for many people too because of such massive wipeouts of funds.