Applications are never fully deleted. The menu from the Apps page has a "delete" option that moves the application to an archive. An app can’t be run or modified when in the archive, but it can be recovered at any time.
To recover an archived application, navigate to the group that the App was in. Click the " • • • " to access the menu, next to the "Create App or Group" button on the top left of the screen.
In the menu that pops up, click “Restore” to recover the archived app.