Strong flat means that you don't have enough money, not without it. After strong flat, you still have money. For example, if you close your position by 50%, you will have about half of the funds left.

Breaking the warehouse is forcing the same thing.

Turning over the warehouse means that your account is out of money, but you still owe money to the futures company. This kind of thing exists in theory and should not happen in recent years. This will not happen to ordinary customers. What may happen is also a very large customer (because only futures companies with special customers will always hold positions), so it is possible to meet in extreme cases.