Earlier quoted context omitted.
No. The broker first contacts the investor to allow them to deposit more money to bring up their equity percentage; if thet doesn't work, they sell the borrowed assets to get the percentage up. One feature of margin loans is that you are required to have assets to cover them. A relic of the great depression, IIRC.
Those collateral assets start out covering the loan, but are often invested in the same assets as the borrowed money and will loose value at the same time. So when the collateral no longer covers the loan, the investor gets a margin call and doesn't have the money... then what? Does the broker have any recourse to credit bureaus or courts?
(Actually, I'm not sure what would happen if the stock went to zero instantly and was the only asset in the account.)