Hi,
Only just noticed this thread was posted for 7.5 not v6.
The batch script for uninstalling the patch agent (called uninstallpatchagent.bat) can be found here on your target systems that have the patch plug-in installed
C:\Program Files\Altiris\Altiris Agent\Agents\SoftwareManagement\Software Delivery\{865760C8-27FB-46FA-A87B-E7FC3EFE107E}\cache
This script should invoke MSIEXEC to uninstall the agent by searching through the uninstall strings for the patch agent. Note however that if you have a policy still in place to keep the patch agent installed it will simply reappear if you turn it off (or exclude clients)
The fall back command for uninstalling the patch agent is,
msiexec /qn /x {26C5D274-98EE-4CB4-A3FE-499C406F0E74} REBOOT=ReallySuppress