There are a number of quests in the game that, if completed in certain orders, will cause another quest or item to become permanently unavailable. This mod attempts to remove, or fix these lockouts. Fixes included:
Diplomatic Immunity and Find the Thalmor Assassin: upon learning about Esbern in the former, some Thalmor will come in having captured Malborn. It is highly likely that Malborn will die in the ensuing fight, which will permanently block the latter from starting. With this mod, Malborn, as well as Brelas and Etienne can only be killed by the player, so that the Thalmor Assassin quest can be started more easily.
Ill Met By Moonlight: Bloated Man's Grotto contains a shrine of Talos where a unique weapon can be found, Bolar's Oathblade. If you start Ill Met By Moonlight before entering the Grotto, the shrine and weapon will be removed for the duration of the quest, if you complete it in favor of Hircine, and permanently, if you complete it in favor of Sinding. With this mod, the Oathblade can be found on J'Kier, the hunter who dies shortly after you arrive; it's not unreasonable to assume he would grab it on the way in.
Delayed Burial and With Friends Like These...: Upon either entering the Dark Brotherhood sanctuary for the first time, either during the latter or during Destroy the Dark Brotherhood, the former quest will become unavailable if it hasn't been started, and will fail if it has but has not been completed. This mod makes the completion of Delayed Burial a requirement before the shack scene can begin (You'll receive an anonymous reminder to check out the road between Dawnstar and Whiterun if Delayed Burial has not been started by the time Innocence Lost has been completed).
Mourning Never Comes and Blood on the Ice: Blood on the Ice requires that Tova Shatter-Shield be alive for it to start. However, during the quest Mourning Never Comes, you are encouraged to kill Nilsine Shatter-Shield, which will cause Tova to commit suicide. Since Tova's role in Blood on the Ice is trivial, and completely optional, I've removed the requirement for her to be alive.
Mourning Never Comes and Lost to the Ages: Lost to the Ages requires you to trek through Raldbthar, where Alain Dufont resides, which means you will likely kill him if you go there before beginning Mourning Never Comes. If he dies, the optional objective to kill Nilsine becomes unavailable, locking you out of obtaining Muiri's ring and her as a marriage candidate. This mod makes it so Alain Dufont will not appear until you reach the appropriate stage of Mourning Never Comes.
Rare Gifts (Siddgeir) and Build Your Own Home (Falkreath): Siddgeir usually requires you to bring him a bottle of Black-Briar mead before he'll begin the Thane quest. However, if you progress far enough to receive the Build Your Own Home letter from him, this will be skipped. This mod removes the Build Your Own Home letters altogether so that this cannot happen. From what I could tell, they only existed to give people who installed HearthFires mid-game information on how to obtain the new homes, so they are unnecessary for future runs.
The Forgemasters Fingers and Being Blood-Kin: If you complete a quest that leads to you befriending an orc, you will be unable to access The Forgemasters Fingers. They will now be sent to you after becoming blood-kin by any means, with a letter explaining why.
Kill the Bandit Leader (Annekke) and Kill the Bandit Leader (Brunwulf): These two instances of the quest draw from the same pool of targets, which means that they could choose the same target. If this happens, the second version you attempt to start will be permanently be unavailable. This is due to the fact that the quest cannot choose cleared dungeons for its target. This mod allows this quest to choose cleared locations and adds code to provide a new boss if this happens, although it will not reset the dungeon. (Note that this situation is very rare and can only occur by chance, so this fix is untested. The theory seems sound enough though).