I don't think it's permanent, but it's a lot deeper and hard to climb out of than USC fans realize. The playoffs have completely changed the recruiting landscape. Clemson walked in there and took the #1 QB in CA this year. The coaching instability really hurts recruiting, too. Guys don't want to commit when they know changes will occur and they won't know their role 2 years out.
The glory days are fading from the collective memory of the kids they are recruiting and that is not good. They are lucky because they are in a recruit rich territory, but as Texas, Florida State and Tennessee have shown, geography alone does not make you immune from falling off. Plus, in light of their admissions scandal, USC athletics is going to get a lot of scrutiny from compliance types. So while guys like Malzahn or Jimbo might be able to get a marginal recruit in on a wink and a nod, USC seems likely to me to be a program where the ivory tower eggheads are going to exercise additional control over the whole athletic department.
I'm not saying they can't get back to championship caliber, but in an era where they will have to beat Oregon and its Nike money and then turn around and beat two top 4 teams (likely OSU or two southern teams) in a row, the path back to the top for them based on the new landscape is really bad. The other factor that can't be discounted is that while the Big Ten Network and SEC Network are printing money, the PAC 12 Network is utter garbage and has virtually no penetration. The start time for their games is bad for most of the national TV market. The SEC is rumored to have just sold one game a week for $300 million to ESPN, which is probably more than the entire PAC 12 media package is worth. The negotiation for their expiring tier one game rights is huge and may even be an existential crisis level for the conference. The lack of marquis games that draw the level of attention of the Iron Bowl, OSU-UM, World's Largest Outdoor Cocktail Party, Red River Shootout, etc. does not bode well for the conference and will hurt USC relative to the teams it has to recruit against.