We were told that there would no longer be updates for System Center Endpoint Protection starting 7/14/2015.

We are monitoring XP endpoint systems and they are still obtaining virus signatures, which match our Windows 7 systems. We also verified the ability to detect a virus that was released after the 7/14 date (on an XP system with System Center Endpoint Protection).

Should we expect to continue to receive virus signatures but not updates to the endpoint protection client? We are in the process of removing all XP systems, however the ability to rely on virus signatures during the upgrade process would be great. 

You should open a support case with Microsoft Customer Support Services on this.