Wave best practice is to "cancel" initiatives or actions, rather than use the delete option. This will ensure that your card is still accessible for reference purposes and can easily be restored if needed.
Cancel an initiative
To cancel an initiative, go to your "Initiative Stage Gate" field (sometimes called Status or Implementation Level), select "Cancelled" from the dropdown, and press Save.
Cancel an action or milestone
To cancel an action or milestone, go to the "Status" field, select "Cancelled" from the dropdown, and press Save.
Restoring an initiative or action card
The same process is used to restore an initiative or action card. To restore an initiative, update the "Initiative Stage Gate" to an active stage. To restore an action, update the "Status" field to an active status. Be sure to save before closing.