It seems nobody could survive the dark brotherhood, not even the emperor with 30 special units protecting him. So lorewise has anyone actually survived the brotherhood?

The Nerevarine
The Dragonborn
Probably others

The Nerevarine wiped out the Dark Brotherhood operations in Morrowind and survived at least one, possibly more assassinations...

In Skyrim if you do certain things in the right way, you can also be the target of a random DB assasin who you can then kill and you will never hear from the DB again (which is odd)... Also, they might still recruit you later on.

In the first situation the DB kept on attacking you, until you wiped them out in Morrowind, so why they wouldn't do so later on is beyond me (though the near destruction of the organization might count for something)... More to the point, I can't remember if the assassination in Tribunal is off because you killed the DB in Morrowind or because Helseth calls it off, I think it's the second. Which at least implies that the DB is willing to completely destroy itself to fufill even one accepted contract.