List of Expired Merge Subscribers
Open SQL Server Management Studio
expand instance of SQL server
expand Replication Folder
expand Local Publications
Right click publication that you want to check for any expired subscriptions and choose 'Launch Replication Monitor'
expand My publishers, right click on publisher in question and click 'Configure replication alerts'
Choose 'Replication Warning: Subscription expiration (threshold: expiration) and click Configure
select Response and check Notify Operator
Add new operator


This will alert you when you have expired subscriptions. It will show all expired subscriptions in Replication Monitor on the Subscription Watch List Tab. If you set it up correctly, will also give you email alerts.

EDIT:

In order for you to receive emails, database mail must be configured. 


Connect to instance
expand the management folder in object explorer
right click on Database Mail and choose configure database mail
add profile name and click Add to configure email address and email server 


if you don't have an email server you can use google / yahoo /etc.



Hope this helps!!