I don't think Nico is going to break them up; Xavin and Karolina's relationship in YA/R makes me think they won't be together that long, anyway. And from YA/R, the first real interaction between Nico and Karolina since Karolina returned (that we've seen,) there isn't much to show her feeling negative towards Xavin for being with Karolina.
As I've said time and time again: Nico and Karolina are best friends. It hurts, big time, to see a best friend go- add that to the fact that Karolina went to another galaxy with an Alien shapeshifter. And to see your best friend come back with were Alien shapeshifting fiancee? How would that feel, knowing that the person who you leaned on for support wasn't going to be there for you 24/7 anymore?
I think Chase will be off the team for #19 and #20, but return at the end of Dead Means Dead. Then again, from the Chase seen in YA/R...he isn't the same Chase we've grown to love. He's one angry, angry person, and any mention of Gert sets him off.
Looks like the Runaways won't be under the Tar Pits much longer, from the appearence of the Hostel they're in towards the end of the comic.
Xavin's pretty F***ed up, though I love his description on the set-up page:
"Xavin: Child of shape-shifting skrull warlords."
Just seems a bit out of place.
To finish up: YA/R #1 is fantastic. The Runaways still sound like the Runaways without Vaughan, and the art is good (a bit iffy at times).
I love me some Nico. Finally, someone realizes she's hot