There is always the possibility of changing the color to Red for
deleted text. Or if it is a task name, you can always put a prefix on
the line like DELETED or OBSOLETE... I'm sure you can come up with a
bunch of options.
If you are trying to delete a task this way, you can always save using
the Baseline and then show both in the gantt chart. In this case the
deleted tasks will not have a "current" line. Deleting, of course will
also delete any history that may have already occurred on that task.
Good luck.
--dwolf