I don't exactly understand what your hypothesis is. The planet Reach was destroyed before even Halo: CE 'happened.' Therefore, the end of Halo 3 has absolutely no correspondence to Reach. End of story. I don't know how people can connect the two. For anybody that has read the books (which ARE actually accurate, since they were developed mostly by Joseph Staten), it is clear the events that took place. 1st Reach, then Halo: CE then various other stories, none that speak of Halo 3. In conclusion, Reach is YEARS before the events of Halo 3.
[Edited on 06.07.2009 1:25 PM PDT]