Do Kerbals die of natural causes?

So, I got a Kerbal stranded on Mun in my first successful landing attempt. No big deal, right? I'll just figure out this whole "getting there and back" thing, then put together a rescue mission.

The next landing attempt was successful, but somehow I messed up the return trip and ended up in a highly-inclined, fairly eccentric Kerbin orbit. Of course, since this vessel's orbit is inside of Mun's orbit, rescuing this guy should be easier - right?

Nope. I forgot to account for the high inclination early on in the launch and ended up burning so much fuel trying to match it that I couldn't get anywhere near matching the altitude. But this guy's got an apoapsis of just 4 Mm, and a peri of just under 1 Mm. Surely, this has to be the easiest rescue scenario I've got to handle yet.

Of course not. I guess orbital rendezvous and I just aren't getting along. I got the next rescue craft pretty close to, and intersecting, the orbit of the previous one but I'm pretty sure I don't have enough gas left to accomplish the rendezvous and get my guys back home.

So, I figured I'd take a break from all that and look back at Mun. So far, I've more or less been using Tim Taylor logic to increase the amount of thrust and fuel available to my rescue craft in order to give me plenty of room for error adjustments. Certainly by now, this thing has got to be able to make it to a Mun landing and back - let's try to get my Neil Armstrong back home, eh?

The good news is, I got it into Munar orbit. It might even have enough fuel left to effect a landing and get back to Kerbin in one piece (perhaps minus a spare stage). So, I decided to check on Neil. And that's where I'm running into trouble.

Last I saw Neil, he was standing in his EVA suit next to the flag he'd planted on Mun. He's still there. However, I can't seem to find a way to control him so I can bring him to the rescue craft when it arrives. I can switch to his Command Module, which is how I can see that he's still standing next to the flag, but when I click on Neil I have no option to switch over to controlling him.

I've looked around and so far found nothing about Kerbals dying from anything other than a substantial collision with another object. Since Neil is still standing, I'm pretty sure that's not what happened. So what did happen here? Can these guys actually die by being left out in their suits for too long? Apparently, the mission timer in the CM says he's been there for over 90 days!

Solution 1:

Kerbals can't die for any other reason than lithobraking (just like aerobraking, only difference is that you replace the atmosphere with the ground) and a collision with an object.

When you're in control of the command module, try switching to Neil by using the [ and ] keys. Unless there's a lot of debris near by, it should only switch between the module, flag and any kerbals on EVA.

If taking control of Neil doesn't work while you are in control of another object, you can go back to the space center and enter the tracking station. There you will be able to select your kerbal from the list on the left and press the "Fly" button.

The only thing that could prevent you from taking control of that poor kerbal is a bug.

In this case, basic troubleshooting. Reload your save file. If that fails, restart the game. If this fails, well, assume that Neil met the kraken.

You could also try bumping him so some of its variables in the code are changed.

If all fail, well, roleplay it. He died of hunger while you pressed the big red button in the tracking station.