Outright deletion is not the only way to prevent a deviation from showing in your deviantART gallery. If you know you will want to display it again in the future, you can simply hide it using the deviation storage tool instead.
Hiding and Restoring Deviations
Hover your mouse over the "Submit" button to launch a drop-down, then click "Manage Deviations" to open the deviation storage tool. By default, the tool displays a list of all your public deviations. Click the check box beside each deviation you want to hide, click "Store" and then "OK" to hide them. While a deviation is hidden, it remains accessible to you, but nobody else can see it until you restore it. To do so, open the deviation storage tool and click "Storage" to access the list of hidden deviations. Click the check box beside each of the deviations you want to restore, click "Unstore" and then "OK."