Oleanders are generally hardy only to about zone 8 (although there are varieties that are hardier and some that are less hardy). You are in 7b so there should be significant damage and I suspect that a normal winter will kill them to the ground. If you mulch the base deeply they should be able to return from the base in spring. You can scratch the bark with a fingernail to see if it is dead (pecan brown color) or still alive (green to cream color). Check the top branches and work you way down to the base near the soil line looking for signs of life. If you see green beneath the bark then wait to prune until it resprouts so you can see how far back you need to cut the plant.
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