Will DB session terminate when client close DB connection
If the DB connection is closed the session will get an error the next time it attempts to query the database. But will work on subsequent tries as it establishes a new connection.
I believe this answer varies by RDBMS, but to answer you question, I believe the general answer is no. You can however manually kill the session, which should release the locks.
You should commit or rollback your transactions, you should not leave them open.