Supposing someone has spina bifida. will they be expected to live as long as others?

Depends on: Severity. If there were no neurologic deficits, and even many times of there were, then life expectancy will be normal. The complications that lead to neuro deficits early on may shorten life span related to those issues, but not necessarily to the spina bifida itself. If they are completely functional, then most likely normal life expectancy.

Spina bifida: Life expectancy is based on the severity of the disorder. Spina bifida occulta normally does not affect life expectancy. More serious disorders such as a myelomeningocele can be a problem - there is a broad spectrum to this disorder and outcome is based on the severity of the anatomical disorders.