Could Buck go back to a civilized life on the plantation?What I mean by this question is: if Buck was put back into life at the plantaion after the end of the book could he survive there.
This is an opinion question. You need to examine the evidence presented in The Call of the Wild and make your own decision, based on your interpretation of the text.
At the beginning of the novel, Buck has lived a life of luxury on the Judge Miller's ranch, but he hasn't been inactive. He has learned to run and swim and hunt and establish his place in relationship to the humans and animals around him. However, as the quote before the start of the story suggests, "Old longings nomadic leap, Chafing at custom's chain; Again from its brumal sleep Wakens the ferine strain." Even in that setting, the instinct deep within Buck's soul call him to return to the wild, untamed existence that becomes his at the end of the story.
Buck could "survive" if he returned to the ranch after the adventures of the story, but he possibly would not be happy to do so.