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Growing poinsettias is easy when you provide them with the proper care. Here is an article or two that you may find helpful: https://www.gardeningknowhow.com/ornamental/flowers/poinsettia/poinsettia-care-how-do-you-take-care-of-poinsettias.htm
https://www.gardeningknowhow.com/ornamental/flowers/poinsettia/how-to-make-poinsettia-turn-red-make-a-poinsettia-rebloom.htm

It can be somewhat difficult to try and root broken branches. However, if you want to try to propagate the broken stem, use only an inch or two of bare (green) stem with a couple small leaves, or tip cuttings, since these root much easier than the old, woody branches. Stick the cutting into a pot filled with damp potting mix and seal this inside a clear plastic bag. This will help retain moisture similar to a mini greenhouse. Place it in an area receiving bright, indirect light. In about 4-6 weeks, the cutting should be rooted and can be taken from the bag.

Because the leaves are so thin, cuttings usually wilt before the stems develop roots; therefore, it can be somewhat difficult to try and root broken branches. However, if you want to try to propagate the broken stem, use only an inch or two of bare (green) stem with a couple small leaves, or tip cuttings, since these root much easier than the old, woody branches. Stick the cutting into a pot filled with damp potting mix and seal this inside a clear plastic bag. This will help retain moisture similar to a mini greenhouse. Place it in an area receiving bright, indirect light. In about 4-6 weeks, the cutting should be rooted and can be taken from the bag.

As long as it is dark, a basement will work fine. If you have not already read our article on getting poinsettias to bloom, you may find it helpful: https://www.gardeningknowhow.com/ornamental/flowers/poinsettia/how-to-make-poinsettia-turn-red-make-a-poinsettia-rebloom.htm

They really can't tolerate temps below 40F. I would consider covering them if you expect temps between 45F to 50F.

It is best to cover plants with a cloth sheet. Do not use plastic directly as this will harm the plants, though you can cover with a cloth sheet and then a plastic one if you are expecting rain.

I think that as long as you provide the shortened "days" the plants will continue their red leaves. It will require more work to keep them in this state, but that will keep them red until Christmas.