JDRIZZLE15 said: I'm pretty sure Doctor Who could fit into this...
He can't try again. What has happened has happened, especially if it's a fixed point. The old series even named this, something along the lines of 'Narrative Causality': once the TARDIS lands, it's part of the events, you don't get a "Rewind time and retry" like Prince does. Last time he tried to change established history, History took him down a notch by killing the 'Time Lord Victorious'.
Well Homura could have left things as they were as well, but she's still in the picture... well leaving the picture.
She, her lover, and all her friends would have died or turned into witches if she hadn't kept looping until she found a way to save Madoka. That's not really an option.
By that measure, Yuki could have just snapped and done something to cause a critical existence failure, or Rika could have left her friends to die, too.