So i finally managed to get to Deidranna and nail her head to a wall, which causes my mercs to say their piece and the game then to load ...something. It kinda just stays there on the loading screen afterwards with a full bar, doing nothing.

What exactly is supposed to happen after killing her?

You first of all get a statement from each of your mercs, which it sounds like you got. Then it cuts out to a fairly limp cutscene of enrico chilvadori giving a speech about good old american values like being nice and having a democracy.

In the speech he references Miguel and says he looks forward to sharing the ballot box with him again in the future. I don't know what happens if Miguel dies. My plan was to find that out when I tried out Wildfire, but having beaten almost everyone, I shot miguel in the head (very satisfying), but Wildfire doesn't seem to have the end cutscene.

In short, it's a pretty lame end to the game, you haven't missed much. Then you get the credits.

Huh, kind of a bummer, that.

So... who's Miguel? (Enrico is the guy who hired you, right?)

Also: Elliot is friggin indestructible!. o_O
He got shot in the head by Deidranna and was there in the palace when i entered, then got shot by me ("L-lets put him out of his misery...") and the next time i reentered the palace (didn't find the entrance to Deidranna's hideout at first) he was there again.

I totally need that guy on my team.

Miguel Cordona is the leader of the rebels, he's the one you give the letter to at the start.

Couldn't say about Eliot's Indestructability, I tend to offload a burst fire at close range into his head for a laugh, and that always kills him.