Umm...it sorta blends into a new storyline and then into FreeLancer, it doesn't really 'end'.

Yeah after you blow up the coalition station, and the massive worm hole generator/ship the story kind of just drops off to a "Good job! We got Jupiter, and they are retreating, and were regrouping! Have a cookie!" all in a cinematic of Eneiquez talking about it to you in the briefing room.

Oh and Claus Steiner is killed by that surviving Petrov, after he rams something with his fighter, and ejects.

Wouldn't you rather find out for yourself?

But yeah. You go back to the briefing room, Enriquez congratulates the squad, gives you extended R & R, then there are credits, then the main menu. It's kind of an anti-climax really... don't you guys agree? For such a great game to end in such a mellow way? I suppose that because the war was still going on, it's the best way... can't likely have a SW6 ending, but you could at least have a ship-wide party or something... right?

"If it aint on fire, you haven't shot it up bad enough yet" - my old teacher on Planet Housten.

Maybe it's because they were thinking of a sequel back then?
BTW, Steiner does not necessarily die
You actually may save him, then he joins the 45th

An idea came to my head and is now desperately searching for brain

How do you save him? I get a script of him ramming the station!

He ejects . . . What you have to do is stop Petrov from zapping his escape pod.

Ban REVERSE THRUST! Fly something other than a phoenix for a change!