If you don't want them reseeding, and don't need the seeds for trading or planting elsewhere, I'd trim them back as far as the nice leaves. Then they won't droop so much. If the seeds are ripe, I'd throw the trimmings into a small paper bag and let the seeds dry. Then you can trade for other seeds you might like to have, or share them with friends or neighbors.

Martha

Balloon flower (Platycodon grandiflora) does much better (IMO) if it's whacked back to a third of its height early in the growing season so it doesn't grow so tall it flops over. According to my notes I cut most of my plants back in mid-June. All are blooming with gusto at the moment & growing fully upright. There are plenty of seedpods but I haven't decided whether or not to harvest seeds this year since I'm not committed to growing more of them via winter sowing. I may harvest seeds only from the double white & double blue varieties.

Be aware the term bellflower is generally used in describing campanula rather than platycodon. Larry Hodgson's 'Perennials for Every Purpose' describes them as "kissing cousins" but in my garden campanula blooms much earlier in the season than platycodon/balloon flower.

You can certainly deadhead them if you have no interest in the seedpods or harvesting seed. I generally just leave them for the critters who might benefit from the seeds. Whatever you decide, it's your garden so do what pleases you.