Cleanup of Oracle killed session
I think this expected behavior for an inactive session that has been killed. 

I have a session connected as a user 'JAY' which is in 'INACTIVE' state.

 [oracle@myserver datafile]$ sqlplus jay@hrpdb
 Connected to:
 Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production


Let's check session details using sys user. 

SQL&gt; col username format a20

SQL&gt; select sid,serial#,username,status from v$session where username ='JAY';

       SID    SERIAL# USERNAME             STATUS
---------- ---------- -------------------- --------
        15      36102 JAY                  INACTIVE


Let's kill it. 

SQL&gt; alter system kill session '15,36102';

System altered.


Check session details once again.

SQL&gt; select sid,serial#,username,status from v$session where username ='JAY';

       SID    SERIAL# USERNAME             STATUS
---------- ---------- -------------------- --------
        15      36102 JAY                  KILLED


It is still there in 'KILLED' state. 

Now let's try to do some operation in Jay's session which was inactive and killed.

SQL&gt; select * from tabs;
select * from tabs
*
ERROR at line 1:
ORA-00028: your session has been killed


Now let's check session details using SYS user.

SQL&gt; select sid,serial#,username,status from v$session where username ='JAY';

no rows selected


The session is no longer visible in v$session.