If you leave the password the same, they will just sign in again. It is just human nature! Also, they will still have access from their mobile device. Also, when we have users on leave, we usually use Delegation to the users manager instead of forwarding. It's an option. We also have a status custom attribute set up with date, OU, and description... where we record the on leave date, On Leave or Terminated, and the OU
Our on leave process:
Sign the user out
randomize the user password
deprovision the user
remove mobile devices from the users account
add manager as delegate
add access to calendar for manager
map calendar to manager
create OOO responder
update custom status fields