If you go on youtube, you can watch the trailer for Halo 5 which was played at E3 this week...and in it you'll see John with a dog tag with Cortana's chip on it--so this scene technically COULD happen! They must have retrieved her chip from the debris. Ah, the feels!! The FEELS!! This is a great piece of artwork! Good job!!
this scene has already happened. in the end of halo 4 the chief looks out at earth from the orbital platform and talks about how cortana once told him to figure out that which one of them was the machine.