If the customer fails to add the margin within the specified time, the ownership of the transaction will force the customer to close his position. Futures are different from stocks. Futures have a time limit. Expired contracts are either delivered by the exchange or closed by the exchange, so it is impossible to keep them forever.
Moreover, individual investors are not allowed to enter the delivery month, and the profits from forced liquidation will be transferred to the exchange, so customers should pay special attention to the delivery month when doing transactions.
If the contract does not expire and the available funds are not less than 0, the warehouse can be kept all the time.