I need to grant object privileges to a user but I'm not the owner of the schema.
I've tried doing it with the System user but I can't either. My long shot was using the Sys user (other than System) but it is deactivated and there is no way I'll be able to activate it with my user.
Is there any way I grant that privilege to a user? I can't ask the owner of the schema to do that because she resigned today... and I don't wanna change the password of her DB user.
I know that at some point I'll need to create a new DBAdmin user and create a backup of those schemas because when the SAP user of my colleague be deleted, it'll delete the Hana user and the DB user with all of the objects, roles and privileges created and granted with it.
Oh oh! Be very careful here with the deletion of the user since - as you correctly write - the deletion will have a cascading effect.
Also: you have to either have the ownership for the objects OR the privileges you want to grant with grant option. Using the SYSTEM user won't help with that and SYS can never be used to logon to the database anyway.
Since there is also no way to take over ownership, the only actual way really is to find out which objects and privilege grants the user has created/performed.
Then logon to the user and refactor the grants to roles that cover the object privileges. As a next step, you may consider creating a non-logon user to own the objects and then perform a import/export of the users' objects.
Finally you may create design time roles with the required privileges to the objects. This allows granting/revoking of the privileges by a user with the ROLE ADMIN privilege, which makes management a lot easier and better structured.