It’s so rare that I disagree with BFNE, and I don’t know why I care all that much about this, but I did a little surfing about CO helmet anatomy and it confirmed that the padding around your head is independent of the shock absorbing layer of the helmet:
"Directly beneath the shell is the expanded polystyrene or EPS, the part of the helmet that absorbs the energy of the fall so that the brain does not bruise itself inside the skull. The polystyrene layer is made up of thousands of beads that are full of tiny air bubbles.
…
Inside the expanded polystyrene is the inner liner, which includes the comfort padding and sizing foam."
See http://useventing.com/news/behind-charles-owen-badge-helmet-materials .
Obviously, your helmet may need to be replaced if the padding is packed down, but it may need replacing even if it isn’t. The questions are independent.
Lucky thing for me, because I don’t really want to buy a new helmet. 