Infested Valerian: Another Idea for How I Would Do SC2 (SPOILERS)
Here's another idea I had pursuant to how I thought StarCraft II: Heart of the Swarm should have gone. In a discussion on my message-board, the user whose handle is yorel said that Arcturus Mengsk would not deliberately kill Valerian. If Valerian were sent in to negotiate Arcturus's surrender, he might imprison him or use him in some kind of scheme (like sending him back with Nova and other Ghosts on his tail). I went and edited my post accordingly just to have Valerian die, possibly by accident, so the Terran Dominion would splinter into civil war and much of it would follow Arcturus into service of the undead Xel'Naga Amon, the Dark Voice.
Valerian doesn't have to die, but he could be mortally wounded and to save his life require Sarah Kerrigan to infest him. Since in my scenario involves Mengsk fleeing to the Dark Voice with the Xel'Naga artifact as a potential genocide weapon against both the Zerg and Protoss, this can't be undone once Valerian has physically recovers.
Now any attempt to set up Valerian as the new emperor of the Terran Dominion is going to kick off a civil war. Not only are Raynor and Valerian blatantly in cahoots with the Zerg, but now Valerian is for all intents and purposes a Zerg himself. Even if Kerrigan's infestation preserves his mental independence, people will think he's under her control. And Kerrigan is the Dominion's public enemy number one. Rather than a revolt against a tyrant, it's become the Zerg taking over the Dominion. However, Raynor has enough following that there are many people who would side with him, especially since he revealed that Mengsk Sr. was responsible for the Zerg obliteration of Tarsonis.
However, this leaves Valerian alive rather than killing him off. Although he appears in other Starcraft media, Starcraft 2 ( in particular, Starcraft II: Wings of Liberty) is his first game appearance. He's too important to bring him in briefly and then kill him, as ends up happening to General Horace Warfield. It could also sow conflict for Arcturus in the upcoming Protoss story Starcraft 2: Legacy of the Void--if he realizes his son is still alive and infested, he might be tempted to use the Xel'Naga artifact to de-infest him rather than whatever the Dark Voice wants him to do with it.