Rollback from what, the installation? Deleting the toolbar you create when
the Inspector or Explorer closes plus declaring it as temporary when you
create it is the usual best practice. The usual setting of all objects to
null (Nothing) when the procedure where they are used should be done, as
should removing any event handler in the Close event. Beyond that I usually
get rid of my global or connect class Outlook objects in my Teardown()
method, called from Shutdown() or Explorer.Close() when the last Explorer
closes and there are no Inspectors, by calling Marshal.ReleaseComObject() on
each and then calling GC.Collect() followed by GC.WaitForPendingFinalizers.

Any files added during installation or registry entries added during
installation will be removed by uninstalling. Anything added on the fly
should be removed using custom actions.