As for the short position, it means that your floating loss has exceeded your customer's rights and interests, which means that even if you close your position at the current price, there is not a penny left in your book.
But under the current supervision system, the possibility of warehouse explosion is almost zero.
Your other questions:
1, yes
2. No, buying futures is taking up margin.
3. Yes, forced liquidation is to flatten your position. The margin released after liquidation will be returned to your account, but the loss will be deducted. If the margin balance is not enough to make up for the loss, the futures company will recover the rest from you. If you don't make up, you will face legal proceedings.