It's an annual, Vero, so the original plants are dead. You did the right thing leaving them, as they normally seed themselves and your garden will never be without them. However, I find that the best one for self-seeding is the pale blue one - 'Miss Jekyll'. Some of the others don't seed so freely. You might have to buy a new packet of seeds if that's the case.

You can pull up the dead plants now, by the way!