She definitely would have too much pride to just get up and run away. And while she isn't exactly parent of the year, she wouldn't take off on her remaining kids. Tommen in particular is like a power nestegg, and leaving him to the Tyrells would be a huge no no, abandoning too much satisfaction on them. If anything, she would rather destroy Tommen herself than any "enemies" have him.
But, it would kind of interesting. For one thing, I'd be curious of her journey and diabolical plans. For another, it would be kind of ironic: The previous Queen before her was forced to run from KL and hide, thanks to the Rebellion with the Lannister's help at the end.
Then again, there are already a lot of people on the run/living the life of igcognito already, so maybe adding Cersei to the mix might be overkill.
Edited by Melpomene, 24 October 2012 - 10:35 PM.