Can I show a relation - "Either in this table or in that " in ER diagram? I am making a database for handling leave applications in an academic institute. Given that there is hierarchy existent in such institutes, and I need to keep record of the people that were at these posts, say 'Dean', I have implemented a table 'archived_cross_cutting_faculty' in addition to 'current_cross_cutting_faculty', where cross_cutting_faculty means the guy is dean or something else in addition to being a faculty.
To have a record of retired faculty, i have table retired_faculty in addition to faculty table.

Now, the faculty listed in archived_cross_cutting maybe a retired faculty, hence he maybe in the retired_faculty table. Or he maybe present in the faculty table, i.e. he is currently serving as a faculty but say, he is not a dean now. 

Can this relation be shown in ER Diagram? That a person in archived_cross_cutting_faculty is either in the faculty table or in the retired_faculty table? How?
In the ER model,  this concept is known as Generalization/Specialization.  A diagram illustrating this is shown in the artcle linked to. 

https://www.geeksforgeeks.org/generalization-specialization-and-aggregation-in-er-model/

A word of caution is in order, however.  Gen/spec is applied to Entities, not tables. The difference between entities and tables is in the level of abstraction.  If you want to think clearly about the subject matter,  and not just the database, it behooves you to keep the levels distinct in your mind.
An entity is an object in the subject matter whose descriptive data may be stored in a table.