In order to get EM working when publisher is down, you can either use SLB based solution to provide redundancy for CCMCIP and EMApp, or follow the steps below:

1. Configure DNS alias to include at least both pub and sub.

2. Create a new IP Phone service that points to subscriber EM app.

3. Modify the IP Phone configuration to subcribe to both publisher EMApp and subscriber EM app.

When publisher is down, end user will see some delay (about 30 sec) for service to return. End user will need to select the subscribed service on subscriber for EM login/logout.

http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_tech_note09186a0080093e72.shtml