A sleep number bed should last as long as any other bed as in between 10 to 20 years depending on how well you care for it.
I never keep a mattress or any bedroom set including the bed frame for more than 10 years because 10 years is a pretty long time.
After 10 years I want to redo my bedroom and get a brand new bedroom set.
My mom has a sleep number bed that is 10 years old and it's still in very good shape and she plans to keep the sleep number bed until she dies or goes into a nursing home.
So she should have the sleep number bed for another 20 to 25 years unless she changes her mind and gets a new bedroom set.
The sleep number bed is a really good quality bed and mattress though so you should get a minimum of 10 to 20 years out of the sleep number bed.