Actually Reach was glassed and Captain Keys fled using the Cole Protocol which requires you to jump randomly away from Earth and by chance, their first jump landed them at Halo, which is when the first game started. And Master Chief didn't die on Reach. While the fall of Reach was happening there were about 7 of the original Spartan team alive, 6 on Reach and John (Master Chief) on The Pillar of Autumn.
[Edited on 08.09.2010 3:08 PM PDT]