Coleman was rumoured to be leaving the series earlier this year although nobody on the production team were willing to comment.
An unnamed source reportedly told the Daily Mirror:
Supposedly Clara will now be a mainstay in the TARDIS until at least half way through Series 9, after Coleman enjoyed her time on set with co-star Peter Capaldi.When it came to Clara they had to tear the scripts up and start again. In the original draft of the script, she became an old woman who then died with the Doctor at her side. But after they were rewritten, she will now be seen returning to the Tardis, hand in hand with the Doctor.
Clara will, of course, return on Christmas day in Last Christmas in the provisional time slot of 6:15pm.
[Source: Mail Online]