Q.What is the life span of pampas grass
I have 30 year old pampas grass plants that are in shade and are not performing well. Should these just come out?

Pampas grass prefers sun but will tolerate partial shade. I would move them to a new location if you would like to keep it growing.
Digging up Pampas grass is no easy task, but may be worth it to keep your showy plumes blooming.
I have listed a few links for you.
https://www.gardeningknowhow.com/ornamental/foliage/pampas-grass/growing-pampas-grass.htm
https://www.gardeningknowhow.com/ornamental/foliage/pampas-grass/pampas-grass-removal.htm