During my last mission in my most recent campaign (flying a Parasol) I was attacked by an Albatross and shot up pretty badly, but was not wounded. The enemy plane also barely clipped us (I got a collision message, but no apparent damage to either aircraft). I landed in a field on my side of the lines and didn't run into any trees or fences, checked my health status and it was still at 100%. I didn't exit immediately as there was a nice battle still raging overhead and I wanted to see how it turned out, so I waited a about a minute or two until it was over and then exited, only to find that somewhere between exiting the sim and arriving back at the manager that my pilot and his observer had somehow been killed! The mission details had the remark "Dest. by Self". next to my plane. What is that supposed to mean? Fortunately it wasn't a high time pilot and I really wanted out of that Parasol squadron anyways, but that's not how I wanted to leave.

Destroyed by self can occure when you drop bombs while you are at the ground, or if the explosion also takes you with it. Or if you are on the ground with a damaged AC and sooner or later it catches fire or something like that.

I was on the ground with a damaged aircraft, but none of the above happened. Fine when I left, dead in the manager.

Various reasons, some as above but a collision could be part of it as you later died of wounds. When you land and you seem OK there is still a chance you die later.
As it happens once in a blue moon, maybe use your imagination, maybe as you climbed out with a gammy leg you tripped and crackd your head on the gun. There are 1001 ways to die not included in the sim

Yes, another life lost in such a senseless way. I was close to the front, stray artillery shell. But clarify something for me please, I can still die of wounds even if when I toggle on the status display pilot health reads 100% when I exit? I've died with 98% health after hitting a fence, which is fine, I was the luckless fellow that had a tiny chance of dying from a tiny wound and went and died anyway, but dying from a wound I didn't get? It seems like a bug. Or is there really a chance I could die after every single flight no matter the outcome?

You shouldn't die at 100% no. Maybe something happened just after that you didn't notice. Slow collisions into fences should be fine but as always there's a risk as it represents many types of fences, fields etc.

Right, I only mentioned fences to note that I had experienced the once in a blue moon chance killing me, no fences were involved in the flight in question. I am absolutely certain I had 100% health when I exited. Also, when I have been injured in collisions or wounded in other ways, it always says in the post mission details that I was killed by enemy action, or something to that effect, not dest. by self. I suspect it has something to do with the very minor collision with the Albatross being incorrectly figured in to the chances of my pilot dying.

Or, as I think of it, could it be tied to my observer's health somehow? I don't know what his status was. He was still tracking the Albatross with his gun once we landed, but we took a lot of hits and he could have been badly wounded.