Yes. You can always choose to reactivate the Gift Cards and Credit Memo Plugin. However, there are 2 possible scenarios here.
Scenario 1: Your deactivation date is BEFORE the end of your current billing cycle. In this case, you just need to put a tick on the checkbox on the “Gift Cards and Credit Memos” Plugin Tile and the Plugin will get activated.
Scenario 2: Your deactivation date is AFTER the end of your current billing cycle. In this case you will have to again subscribe to the Plugin through the normal subscription process.