The squad dies if the position is destroyed and you don't get out. They are good in certain situations, but 60 muni is a BAR or zook or m1919 so you often don't really want to upgrade the fighting position.
I've seen them survive it before.
I wouldn't upgrade it though that's for sure.
EDIT:
Also rifle grenade from RE squad ignores line of sight and firing arc. They can shoot it over trees and everything. As long as one of your units has LOS.