John Cena is the greatest superstar in the modern era according to several WWE Officials and he has been the face of the WWE for the past decade. For the past few years, John Cena has focused more on his hollywood career than his wrestling career. Even though he is not completely gone from WWE, he has been wrestling for only limited dates now and he has recently been billed as a “free agent.” 
Even though John Cena has been billed by WWE as a “free agent”, his inclusion on SmackDown’s roster against Raw at Survivor Series leaves some gaps and questions in the storyline. According to reports, the company will be explaining that on TV this coming week. In this day and age, Vince McMahon doesn’t really care about these sort of gaps and questions and evidently it doesn’t seem to have any effect on business either.
The current plan is for John Cena to return to WWE TV as part of the Raw roster after Christmas and begin a program with Samoa Joe.

Source: Wrestling Observer Newsletter