Voted best answer
First as such no deleted objects cannot be restored. There is as such no Recycle Bin. You need to have afw backups to import those particular objects.
If the deleted objects are user-defined, then relevant afw backups can be used to restore using Import/Export tool.
If the deleted objects are default that come from system extensions and you know which object has been deleted, then those can be imported from their installed location. Mostly you will find them in C:\Program Files (x86)\ABB Industrial IT\Operate IT\.....For Example. C:\Program Files (x86)\ABB Industrial IT\Operate IT\PLC Connect\import.
And incase plant is not running, then you can unregister the that particular system extension, that will come in System Extension Maintenance in Conf Wizard and thenm you can load.
Hope it will help you.
As mentioned by first answer; you must restore from a backup.
Unless you want to load a complete system backup (which requires system to be shutdown & deleted) you can attempt to restore bits & pieces using the AfwImportExport tool.
ImportExport has a lesser known feature called "Locate..." that can lookup the correct AFW files (a backup has many...) if you specify search criteria matching your lost data (aspect name, object name, etc.)
Please note that import must be made in dependency order. E.g. you should import an object type BEFORE any instance of the type or the Log Template before the Log Configuration.