[quote=@ManoftheNorth]
<Snipped quote by Kal-El>

I probably, shouldn't have used the wording, I did as it is very story-teller worded, but as lore states when all members of TDB die, they enter the Void becoming one with Sithis, this is stated by all, and believed by all who are truly religious to the beliefs of TDB. Even before TDB was created Sithis was a known entity, he is the void, the ever present Primordial that was present in the beginning, and will be present in the end. The "Wrath of Sithis" was also a presence from before TDB and will continue to be one unaffected by the changes in TDB. This will relentlessly hunt all members who attempt to leave. They are destined for the void, the final debt and the final mark, is always themselves. No matter the escape, no matter the pyschological state, no matter the present province, he will be hunted by the Wrath of Sithis, and returned to the Void. One cannot leave TDB. No one has ever left, not even characters like the Champion of Cyrodil and The Dragonborn can escape the fate, without aligning themselves with a Daedric as CHAMPION. Thus, Tyrion would be dead by now, long be now.
[/quote]

Actually wrong. In Oblivion, it shows that the Wrath of Sithis is a wraith and the Hero of Kvatch can defeat it three different times to which he is closed off from the Dark Brotherhood forever. In Elder Scrolls lore, besides the very beginning, Sithis has never once shown himself or did a thing. It has all been the will and worship of others saying they are carrying out his duties. The Night Mother is the only person to have spoken with Sithis himself but beyond that Sithis has not done a thing. You can say that the wraith is from Sithis as it is known as the Wrath of Sithis which makes sense. 

I cannot find a single thing that states you can't leave the Brotherhood except for the Shadowscales which are killed if they leave. Enric Milres, character in lore, left the Dark Brotherhood and was only killed because he wrote book giving away Dark Brotherhood secrets. To my knowledge from research is you have to fight the Wrath of Sithis to earn forgiveness and if defeated three times then you gain forgiveness and are safe. You only envoke the Wrath of Sithis IF you break the tenets.