This is a interesting question. The QlikView dashboard on the server will have a file in the same folder with the dashboard name and with an extension of .shared.
All the bookmarks of users are stored in this file. Ideally there will be no impact because when the user leaves the shared file would be as it is. Also once the user shares the bookmark then internally it will store the user id for whome the bookmark was shared with the bookmarkname and teh selections.
You could use QlikView Powertools to view inside the .shared file.
Logically there will be no impact. Its just instead of whole team creaying the team lead creates the bookmarks for the team members.
As Rajesh said that the Shared Objects created by any user is stored in Shared file and it won't get deleted, but as you said that the user is going to leave and his/her account will get deleted so in this case might be the object won't be visible to the user and it will comes under the corrupted object list.
Inorder to restore that shared object you can contact the Admin (Who have admin access of QMC) , he can change the owner name of that shared object and hence no impect will be there on that object.
Also he can open the shared file with Shared Object Handler TOOL and can change the owner name for the respected object.
NOTE:- In order to doing anything with shared file please maintain a Backup.
Just a note:
Changing the "Ownership" of the Bookmarks made them unavailable to their original creator (the User has not yet left the Company) - even though they were still available to those Users who has "subscribed" to them.
So, for now, I have reverted back to the original ".SHARED" file - and will address this again once the User has been removed from Active Directory.