How to get the Microsoft CRM “Closed Activities” Nav Bar Link Back (if you delete it)

Just export the solution of entity and add following relationship

<NavBarByRelationshipItem RelationshipName="Contact_ActivityPointers" Id="navActivityHistory" TitleResourceId="Tab_Label_History" Icon="/_imgs/ico_18_history.gif" ViewId="21E2B905-6FDB-470d-8517-AD69B4C01268" Sequence="20" Area="Info">
<Privileges>
     <Privilege Entity="" Privilege="ReadActivity" />
</Privileges>
<Titles>
<Title LCID="1033" Text="Closed Activities" />
</Titles>
</NavBarByRelationshipItem>

Here I have set the example of contact entity.