She obviously metabolized it. I think that is why she was able to survive in space so long unaided. My theory is she was living off of the life force and energy of all of those heavenly bodies she just devoured. Read this scan from Uncanny X-Men #156:
http://2.bp.blogspot.com/_fk08_a_AUO...CRE6SukYbqN=s0
Notice when Deathbird kicked her out into space, it was stated that Ororo can only survive for 30 seconds out there without life support. So, the X-Men had only 30 seconds to save her.
Now, lets go to the Brood Saga:
http://2.bp.blogspot.com/TA1J3mXX9Mx...8gMxMFVdjnu=s0
Notice how just being in proximity to all of the heavenly bodies in the galactic core, she was able to feed off of their life energies and draw both spiritual and material sustenance from them. Then, she summons the full power of the core and essentially becomes a star that is sum of all the energy in the core crammed into her body:
http://2.bp.blogspot.com/Z7nv4mGSzvE...QJ8nfYvtl8v=s0 So, she absorbed into herself every iota of energy in that core including the very life force that strengthens her spiritually and physically. Yet, pulling this feat destroys her ship and life support. Remember, she is supposed to be able to survive in space for only 30 seconds unaided. Which brings me to my next point: Uncanny X-Men 166:
http://2.bp.blogspot.com/eUx03oWIP12...B8siTgrPAhp=s0
Notice here that the Acanti found Storm while she was in the last moments of her life. So, she had not yet expired when they happened upon her. Also, the Acanti were not actively looking for Storm when they stumbled across from her. She had to have been out in deep space without any life support for an awful long time...certainly much longer than a mere 30 seconds. My belief is it is the energies she absorbed/devoured from the galactic core that sustained her all of that time up until the Acanti found her. I make this claim because as the Uncanny 165 X-Men scans establish, she draws spiritual and material sustenance from living stars and planet and she had just consumed so much of that life force.
Nowhere in the scans did it state that this was a strain on her body. In fact, if anything, this was the easiest thing for her to do as the very energies she was absorbing actually strengthened her physically and spiritually and was likely how she survived in deep space for so long before the Acanti found her. The Uncanny 165 scan even stated that it was a simple process for her.