Rex's sudden departure shocked them greatly.
It brooded this united intention in the hearts of the Silverstar Pack to show him their worth, to give Rex a pleasant surprise when he came back as their gratitude for being given this new life, and being a part of his future.
All of them wanted to prove themselves.
Rex has always been vying to be the strongest.
His parents are avenged now, and he found it in his heart to not forgive, but tolerate the Humans for the time being, thanks to Giana, and that might change Rex's path slightly. But all of them knew that Rex had the capacity to be ruthless, even to those he held in his regard.
Leaving Rosie behind is the epitome of his cold-hearted ruthlessness.
Anyone who lagged behind will be abandoned.
Rex might not be the same as back then, but that doesn't give any assurance to the others.
And that pushed the others to keep up.
But more than that, all of them wanted to convince themselves that they were worthy of this power.
