I love how people ignore the fact that the screen at the end of Season 12 said "Freelancer Armor," and not "Freelancer Body."
It made two references to the delivery being JUST his armor in that one shot. It said "Freelancer Armor" and "Helmet, Agent Maine."
The Chairman also said he'd be putting "it" in his trophy room. Never once did he, or anyone else, say "Maine" or "Meta."
This is amusing. What we saw in Recreation and Revelation, while not the Meta, can't really be considered Maine anymore. Sure, it's Maine in body, but no longer in mind. You can't seriously expect a person to have 8 AIs in their head and survive the madness with their sanity intact when Caroline was struggling with just two of them and Wash was temporarily driven mad by just one.
And while it is the armor that they collected, that armor was last seen on Maine's body, meaning that there is a possibility they have that as well. And even though it was said he was putting it into his trophy room, we find out later that he has bigger plans for the suit.
'And that Maine was very, very dead. Drowned.'
Doesn't really matter in the Halo/Red vs. Blue universe. Sarge gets sniped in the head and gets revived by CPR. Those sniper rounds are armor piercing so by all rights even with the later revealed armor lock he should've died. Maine/The Meta himself is ridiculous, surviving things he shouldn't up until that drowning.
Even Halo isn't above this. Linda (The co-op spartan in Halo 1 and 2) in the story proper got ambushed by Covenant and suffered many plasma hits including one to the back of the head. She was basically killed and they cryogenically froze her until in-between Halo 1 and 2 where Catherine Halsey shows up and flash cloned her kidneys and a liver of all things, as if that's all that was wrong with her.
So yes, I'll believe that Maine has "died". But that doesn't mean he can't come back at a later point, especially since Charon industries have dabbled in cryogenic freezing.