The lifespan of poinsettia plants depend on whether they're outdoor plants or indoor plants.
Outdoor poinsettia plants can live for up to 2 years with proper care and watering while indoor poinsettia plants have a much shorter lifespan and the lifespan of indoor poinsettia plants are measured in months and not years.
The average lifespan for an indoor poinsettia plant is around 6 months but sometimes they may only last for 6 weeks.
Make sure to allow plenty of sunlight for the poinsettia and water then at least once every week and they should easily thrive for at least 6 months.