And here I thought the last few steps leading up to an apocalypse were non-obvious. The good guys in the actual books will go the pre-commit to destroy the world route, but the White Hand chose instead to weaken the presence of magic in the world to stop the escalation from going too far, which also stopped the nuke (temporarily). Until then the nuke is used over and over again, and the White can't really stop it short of spreading themselves thin and keeping their leaders in protected locations, of which there are very few. Oaths plus mind reading do make for wonderful games of Chicken though, and will certainly feature.

The White do have personal goals, but their main goals are to keep the world from getting destroyed and to take down the Black, by any means necessary (And prevent any other psychos from arising, I guess). Making the Black take Oaths would be insufficient as they could be freed from their oaths in their sleep by someone sufficiently skilled with the soul destroying magic. Realistically they must have their souls destroyed so they can't be resurrected.

Memory erasure can be done perfectly with the soul destroying magic, but such skill is rare, and more commonly you simply rewrite the brain with subtle mind control. Technically possible to reverse, but possible like brain surgery was possible a hundred years ago. Ie, success rates are not great, and when things go badly the mind does not fare well.

My world does distinguish between the soul and the brain, but it gets technical and spoilery. Think of the soul as a sufficiently good copy of the brain that you could remake a destroyed brain from the imprint it made on the soul.

The Black has some ability to detect spies. Not perfectly, but as they have access to supremely effective mind reading they can race along with your stream of consciousness, as well as dig into your memories as well as you could yourself, and force you to consider scenarios and thought experiments, and force you to contemplate actions. This is resource intensive, so there is no way they could check everyone all the time, but crucial personnel can be checked hourly if necessary, and the Oaths leave a visible enough mark on those who swear that you couldn't have sleeper agents pass an inspection by the most powerful mind readers. Such mind readers are far between though, so the spies are certainly a fantastic advantage, and carefully worded oaths can wreak havoc where less skilled mind readers can be fooled.

Thank you for your time!