I have read that leaving the pods to dry and split open (so the seeds fall to the ground) is fine, if you want the flowering in the same place.---On the other hand (I have read) planting seeds afresh should be done after the frosts have gone-----How on earth will the seeds survive if adopting the former method of letting them drop to the ground?
Not all will Ken. After they have dropped the seeds you can cover the ground with straw or a fleece( not a tarpaulin or plastic membrane) to help them survive. Or Save the seeds in a cool dry place and plant out come spring. I do that with Lupins and Poppies.