Outlook.com contacts are also synced with other Microsoft services like Skype, OneDrive and so on.
In case these contacts are accidentally deleted, they can be easily recovered (the only limitation being that their deletion can’t be more than 30 days ago).
Here is how :
Login to Outlook.com and choose “People” from the grid menu.
Next, go to Manage > Restore deleted contacts.
The list of recoverable contacts will now be displayed, select the ones to be restored and hit “Restore”.
These contacts will now again be visible after being fully restored.
[For recovering deleted emails in Outlook.com, refer to this earlier article ].