(I assume you mean metadata permission changes, not file system or database system permission changes)
A great reference for this is the following SAS Global Forum paper from 2009:
Using SAS® 9.2 Metadata Security Reporting and Auditing Features
What you are most likely interested in is the Audit.Meta.Security.GrpAdm logger (which would note if a user was removed from a group, which would be how the access would be lost of the user was removed from a permitted group) , or the Audit.Meta.Security.AccCtrlAdm logger (which would be a directed change of permissions on an object, perhaps the folder that this table inherits permissions from)
For more details on metadata server loggers, see SAS Help Center: About Metadata Server Loggers
This paper also talks about using the %MDSECDS Security Report Macro to audit security changes.
Carl Sommer - SAS Technical Support