I'm a lead farmer, mother lover!
Ok heavy SPOILERs to follow so if you haven't read the books or are otherwise guarded, don't read, please:
There's a handful of people informed here, and sadly its a really small minority. As stated previously Jun (Not June to some of you), is one of the few legitimately MIA Spartans. Yes, Jun escapes to support Halsey as a bodyguard for her path towards Castle base. We do hear from the legendary commentary that he IS alive, despite there being readings in which Halsey says her bodyguard died. Here's the reality; Jun could have changed hands at some point and is not necessarily the bodyguard that died protecting Halsey. There's a 50/50 shot there but it becomes more apparent that he's most likely alive thanks to the Bungie commentary.
Additionally, people, please stop saying MC is the only one who made it off of Reach. There is about a dozen spartans still alive, albeit most of them are trapped in the Shield world of Onyx. While the game canon does override books, it should still be said that anything not touched on by the games can be referendum via the books for canon. Therein, Halsey and her other spartans (Kelly, and the others) are alive on Onyx; MC is drifting to some unknown planet; Gray Team is MIA; the Omega team (Red team?) From Halo Wars is technically MIA though may be KIA via Reach (timeline is somewhat undescriptive); and Jun is actually MIA as well. This doesn't even go on to say that production of Spartan-III's may have never stopped. The project WAS a success, why end it?