Cielo's choices after the airport
So, right after the airport, Cielo dies. I tend to be of the opinion that it's suicide, at least partially. This tends to make people go "Wait what why would the happy cheerful cannibal commit suicide" at me. Therefore, have a tiny ramble disguised as an essay.
There are three major things going into this. One, Cielo's highest priority is comrades. He loves his comrades more than anything, and would die for them. If you do not value your comrades to the point of hurting them, he will kick your ass up sideways, and possibly blow his hair at you. (But that's another essay.) And at the time he went up against those missiles, Roland and Argilla had died in the power plant, Heat had died after trying to kill Serph, and Gale had died stopping Angel. Oh, and Sera was dying and he knew that she was dying. And all this happened in a single night. It is safe to say that he did not have a happy mindset. Essentially, by the time this happened, the only one who had a chance of surviving that night besides him was Serph. And Cielo loves Serph, and he knows that Serph loves him, but...he knows he's not capable of replacing the rest of his tribe, and especially Sera, for Serph. And honestly, Serph's not capable of replacing the rest of his tribe for Cielo.
Two, Cielo is rarely as happy as you might think. I've covered this before! And I'll cover it again because he tends to shove it into the back of his head because he'd rather be happy and acting happy is the only way he can normally think to become happy. And it works! Most the time. And there's not a lot in camp that can push him out of this, because camp's a good enough of a place for him that he's a lot closer to being happy than he is in canon. But he hates the real world. It was supposed to be Nirvana, and instead it was a dystopia worse than the Junkyard. (Well, it's not eternally as bad as the Junkyard and it has hope within it, so you know, overall it's really not. But Cielo was there when it was at it's worse, and it was a hell of a lot worse than the Junkyard then.) But honestly? If it came down to a choice between the Junkyard getting destroyed and the real world getting destroyed, Cielo would've picked the Junkyard in a second. He'll fight to save it, and probably would have even without Sera needing to save it, but that's not totally a given. The people in it are shallow assholes and snobs now that most the Lokapala died in the power plant, it made Heat turn against them, the Lokapala themselves didn't exactly give him a good first impression, and I could continue but eh. Staying in this world by himself has less than no appeal to him.
Three. I mentioned this in my last essay on DDS religion, but Cielo's kind of quietly spiritual. And one of the things he quietly believes in is reincarnation, even if he doesn't quite know how it works without the rain (And there is something very interesting about that, come to think of it. In DDS2, when people died, they returned to the sun on its rays. In the Junkyard, the sun never came and the people were trapped in a reincarnating cycle in the Junkyard only, where the rains served as a crude substitute for the sun's rays in the cycle of reincarnation). He has absolutely no doubt that he'll be reborn. His last words to Sera are "Where'd your pretty face go? C'mon, smile! I'll meet you in Nirvana, ja?" He thinks that he's going off to a better life. (And since this is DDS, he's right!)
And don't forget that with the demon virus, he's always going to have to eat people. And Cielo's... relatively okay with it when he's in the middle of fighting for his life, and in camp there's volunteers and it's not like they stay dead anyway (but he's still kinda skeeved out by it), but in peacetime? With no enemies to fight? (As by that time really most their enemies are already dead.) And without Sera's song or the rest of his comrades to give him something else to focus on? Um. I'm not going to say he would or wouldn't survive for long, because I honestly don't know, but I think that he really wouldn't like what it did to him.
Now, I don't think Cielo would've just sat down and slit his wrists after the rest of his comrades died. But there's a distinct difference between slitting your wrists, conveniently forgetting the one thing that just might have kept you alive on a suicide run to keep your comrades safe, and going on a suicide run where there's no chance of survival no matter what you do, but it'll keep your buddies alive anyway. And I tend to think that he's closer to the second of these than the third.