At the moment just before they went down, there was almost no bids in the orderbooks all the way down to $0. And they had almost $1000 million of long liquidations to clear. Those $10M ask walls kept appearing over and over again and nobody wanted to take them. If it wasn't for the downtime, it eventually would of went to $0 on Bitmex perps and their futures.

Would it go to $0 on other exchanges? No idea. It depends what rules the market makers and arbitragers would play by, I am assuming most were out of the market by then and others just simply turned off their algos due to hectic trading action. So maybe it wouldnt go to $0 on those exchanges but the spread would be like $2000-$3000 difference between the 2.

It truly was a very scary moment in trading history, basically what happened when the Swiss Franc removed that EURCHF hedge about 7 years ago.