The format of the show seems fairly standard. The Doctor turns up in his big blue box, sees a problem, and doesn't leave until it's solved. Sometimes the problem is that he can't just escape, largely due to his TARDIS being disabled/in accessible.
But has the Doctor ever just turn tail, and run? Not after solving the problem, I mean just seen things go from bad to worse, and left people behind and retreated? I can't remember anywhere from the most recent series (doctors 9-11).
If this has happened more than once, a good answer might look at why (and not just list episodes).