Help me make sense of the Starcraft 2 ending

Upon seeing that opening vid, I actually thought all marines were convicts sentenced to death and put in the front line as their death penalty. But it seems to me that only Tychus has this deal with Mengsk. In that case, it is safe to assume that it was Mengsk who set Tychus to join Raynor's Raiders.

But in the ending scene, Tychus' orders seem to be actually to kill Kerrigan, not Raynor (I thought he was supposed to kill or bring Raynor to Mengsk). But for that to happen, was Mengsk expecting that Raynor would actually go and try to save Kerrigan? That it was just his convenience that Kerrigan was converted back?

Or was it a huge conspiracy of sorts where Mengsk told his son to get Raynor to help him become his father's successor (much more believable than Mengsk dealing with Raynor himself). I mean it was Valerian who researched and fixed the artifact right? So was Arcturus counting on that for Tychus to have a shot at Kerrigan?

Most marines are "resocialized" former criminals, convicts, etc. with reapers and firebats being particularly egregious villains pre-rehabilitation.

The key difference with Tychus, is that Mengsk knew he had a history with Raynor. Perhaps resocialization engenders massive personality and memory change -- quite simply, if Mengsk wanted to use Tychus to get a pawn into Raynor's forces, resocialization might kill the connection.

So Mengsk needed some other way to ensue Tychus' loyalty. Hence the prison-suit.

What I can't tell you is why Mengsk wanted Kerrigan dead more so than Raynor, especially after Media Blitz. Perhaps the implication is that Tychus was always a spy to Mengsk, and when Mengsk saw an opportunity to hurt Raynor, commanded Tychus to kill her, even if that hadn't been his original intent in setting Tychus free.

On an unrelated note -- without Kerrigan, I'm a little bit confused as to who is going to be the central character for the Zerg expansion campaign. :/

*No information above can be considered canon, and is just the random speculation of a fan.