The parent comment suggests becoming a billionaire through a short. The people who bet long are likely leveraged to some extent, and if they have enough of a BTC portfolio to allow a short against them to make you a billionaire it's not unlikely that they just won't have the money to cover the bet.

We saw this prior to the Great Recession, and in the 1929 crash too. I'm ignoring the potential for a bank run to complicate matters, just sticking with counterparty risk which is easy to model.