They get leggy before they are about to bow out for the season. Chances are excellent that they have left plenty of seed in your pots and the ground too that will come up next year, so be on the lookout for free plants that you can move around then. To get the maximum seed, shake the plants over the areas where you'd like more when you pull them up for the season. It is useless to cut them back. Frankly, I would replace them with a summer annual now.

I already replaced them with summer annuals two days ago. I did put them in the ground and will let them finish flowering and hopefully set seed. Then spread the seed around. My 6 year old has been picking blossoms and drying and pressing them. Funny thing for a 6 year old, but I have been doing the same.