If I didn’t get around to planting a few things this summer, will they die if I leave them in their containers outside?

Regrettably, I always seem to have my share of plants that I just didn’t have the time or energy to get into the ground. If you have a cold frame, potted plants would winter well in one. I do not have a cold frame but have had good luck wintering potted plants over if I trim them back and thoroughly water them once they have died down. Then I put them next to my compost bins and cover them with straw and/or loose leaves. I think the warmth of the compost and the loose mulch keeps them from getting too cold too fast. If you do not have a composting area, perhaps you could try putting them next to shed, preferably the north side, and putting straw or leaves on them. If you have a particularly warm and dry winter, you will need to check the plants regularly and water them if needed. While leaving a plant in its container for the winter is not ideal, there is nothing to lose by trying it if it is no longer possible to plant it.