Title says it all..

Personally I have this really good idea where he lays down the mantle/rank of "Master Chief" to another Spartan so he could finally retire. But I'd think that if John does retire it would be in a way in which he fakes his death as he would finally be done with war at long last. I think it'd be cool if Chief finally got together with Lieutenant Parisa and settled with her at Reach.

Halo as a series started with Reach and it should end at Reach and in a way Bungie did make that happen but then again, Master Chief's story had ended already and he was left stranded in space so 343 ahould try to have a round 2 and try to do what Bungie did but actually include Chief this time instead of some other character.

Only flaw I see with my theory is Parisa hasn't even been introduced yet but I think she should be introduced eventually in order to set the stones for Chief's final adventure.