When you back out a patch, the patchrm command restores all files modified by that patch, unless:
The patch was installed with patchadd -d (which instructs patchadd not to save copies of files being updated or replaced)
The patch has been obsoleted by a later patch
The patch is required by another patch
The patchrm command calls pkgadd to restore packages that were saved from the initial patch installation.
During the patch removal process, patchrm keeps a log of the back out process in /tmp/backoutlog.process_id. This log file is removed if the patch backs out successfully.