So far, we know Percy to be a conceited, pompous, arrogant blowhard with no respect for his family or for what his family has done for him. He works at the Ministry of Magic and is pretentious enough to come to the family only if it helps out the Ministry (i.e. in book six when Percy visits with Scrimgeour). All of this family turmoil between Percy and the rest of the Weasley family makes me wonder if there is any hope for this self-serving office boy.
In my opinion, it would be too predictable if Percy returns to the Weasleys. I don't believe that the family and the Ministry are enemies, in the broader sense of the term, so technically, Percy isn't on the Dark side- yet.
There's been a lot of speculation that Percy will become a Death Eater. This claim kind of makes sense to me, seeing as how Percy likes to be on the "team" with the most potential success. I can picture it now: "Oh mother, it is quite obvious that the Dark Lord will fare better than the Ministry. I could become much more accomplished and successful if I work with the him. The Ministry has been losing immensely, and how would that look if I was part of a sinking ship?"
Then again, Percy is also very intelligent, and clearly has common sense, so although he is incredibly hungry for success, it's also very feasible that Percy will remain on the Ministry's side. I'm only posing possibilities, because Percy here is a sticky wicket.
