Dear Garima,
You need to prepare a "Policy on Handing/Taking Over". It need not used only when a manager quits the company but even when manager proceeds on a long leave. Roughly, managers need to hand over and take over the following:
a) Material assets
b) Confidential correspondence files
c) General policies, folders, registers etc
d) Pending matters with the other departments
e) Pending matters with the suppliers, consultants, advisers etc
f) Subjects on which action is not to be taken (when manager proceeds on a leave)
For the smooth handing/taking over, let HODs of all the departments identify what needs to be handed over when they proceed on leave or separate from the company. Some important registers or folders need to be marked with a notice that "this register is company property and it is to be handed over/taken over properly".
Thanks,
Dinesh Divekar