No, it is not possible to retrieve a deleted feature service from ArcGIS Online. Once a feature service is deleted from ArcGIS Online, the REST endpoint of the service is deleted as well. Without the service endpoint, it is not possible to access the service definition information required to recreate the feature service.
However, if a service definition file is created and saved when the feature service is published, the service can be republished using this service definition file. Nevertheless, this only recovers the original features because any edits that were made to the feature service are not written to the original service definition file. A service definition file can be republished from its Item Details page in ArcGIS Online.
As a precautionary measure, it is recommended for users to enable ‘Delete Protection' on important items before publishing a feature service initially. ‘Delete Protection’ can also be enabled on the published feature service to help prevent accidental deletion. This setting can be enabled through the item details page in ArcGIS Online while editing the item properties. Check the Delete Protection option to avoid having the item accidentally removed from the site. For more information, refer to ArcGIS Blog: Protect and manage your ArcGIS Online content.
Users may also back up content in ArcGIS Online by following instructions provided in How To: Back up content in ArcGIS Online.