• MagicPlot shows legend box if 1) legend is switched on in axes properties, and 2) legend text is present (not empty).
• Deleting legend box on plot is equal to switching off legend in properties dialog.
• Deleting legend text label on plot is equal to setting empty legend text.

To switch ob legend box select axes box on plot and set Legend checkbox in inspector toolbar.

To reset deleted legend for data or fit sum curves on Fit Plot toggle 'Data' or 'Sum' checkbox in Fit Plot window. Legend text will be reset to default and you will be able to edit in on plot.