Missable side quests list and guide
WARNING: this list is still work in progress; use carefully, the list may not be complete and marks may be wrong! It also does not cover their walkthrough, only the things you need to watch out for if you want 100% completion.
If you notice some error or can provide new info, please post.
I gotta say, this game is a nightmare to 100% complete. It's very easy to miss some side quests, so I decided to put up a list of all of them (I'm yet to see a guide that covers every single one from this list, and yet I may have still missed something). I didn't include random events that do not get logged in quest log since they do not impact any type of 100% completion in any way, and I think none of them are missable/failable. At each one of them, I used the following marks:
+: cannot be missed; can be started even after finishing the whole main storyline
!: can be missed by progressing too far with the main story; almost all of them must be completed before going to the Isle of Mists
#: the most annyoing type of missable quests: they will be forever lost if you pass near them without reacting (if you reload the area, they will be gone), or in extreme cases, they will disappear right in front of you if you don't react quickly enough (example: "A Walk on the Waterfront")
*: a special warning about a quest
So basically, if you are a completionist, you'll want to complete the "#" quests as soon as you are able to enter the land they are in. The "!" quests can wait, but be careful: for example, "On Death's Bed" is only available before unlocking Velen.
=== WHITE ORCHARD ===
+ A Frying Pan, Spick and Span
+ Missing in Action
! On Death's Bed (it's available only before unlocking Velen, so make sure to finish it before returning to Vesemir after collecting the griffin reward)
# Precious Cargo
+ Twisted Firestarter
=== VELEN ===
# A Dog's Life
! A Favour for a Friend (must be done before going to the Isle of Mists)
+ A Greedy God
! A Towerful of Mice (must be done before going to the Isle of Mists)
! An Invitation From Keira Metz (must be done before going to the Isle of Mists)
# Bitter Harvest
+ Blood Ties
! Ciri’s Room (must be done before going to the Isle of Mists)
# Death By Fire
+ Defender of the Faith
*+ Fake Papers (do not complete it before triggering "Thou Shalt Not Pass" or the said quest will be forever lost)
+ Fists of Fury: Velen
+ Fools' Gold [DLC only]
! For the Advancement of Learning (must be done before going to the Isle of Mists)
+ Forefathers’ Eve
+ Funeral Pyres
*! Ghosts of the Past (you must simulate Witcher 2 choices and tell Voorhis that you spared Letho, and then you must complete it before going to the Isle of Mists)
*+ Gwent: Playing Innkeepers (make sure to play with Olivier before "Now or Never" if you want to avoid a failed objective)
*+ Gwent: Velen Players (make sure to play with the Baron before "Return to Crookback Bog" or, if you ignore it, before going to the Isle of Mists if you want to avoid a failed objective)
# Hazardous Goods
+ Last Rites
+ Love's Cruel Snares
# Lynch Mob
*! Magic Lamp (can be missed by refusing to help Keira at the end of "Wandering in the Dark" main quest)
+ Master Armourers
+ Races: Crow's Perch
! Return to Crookback Bog (must be done before going to the Isle of Mists)
+ The Fall of the House of Reardon
+ The Truth in the Stars
+ The Volunteer
*+ Thou Shalt Not Pass (make sure to trigger it before completing "Fake Papers" or it will be forever lost)
+ When the Cat and Wolf Play... [DLC only]
+ Wild At Heart
+ Witcher Wannabe
=== NOVIGRAD ===
+ A Barnful of Trouble
*! A Dangerous Game (make sure to collect the green statuette during this quest or you will not be able to complete "The Soldier Statuette")
*! A Deadly Plot (you must accept Dijkstra's offer at the end of "Now or Never" to be able to start this quest)
+ A Feast for Crows
! A Matter of Life and Death
+ A Tome Entombed
# A Walk on the Waterfront
+ A Warm Welcome
! An Eye for an Eye (must be done before going to the Isle of Mists)
+ Black Pearl
! Cabaret (must be done before going to the Isle of Mists)
! Carnal Sins (must be done before going to the Isle of Mists)
+ Empty Coop
*! Fencing Lessons (you must accept Rosa's lesson offer during "Broken Flowers" main quest)
+ Fists of Fury: Novigrad
*! Following the Thread (it is a "+" if Lambert survives the Battle of Kaer Morhen, but otherwise it must be done before it)
! Gangs of Novigrad
*+ Gwent: Big City Players (warning: do not play with Madame Serenity before unlocking Dijkstra or the quest will complete prematurely, likely a glitch, also make sure to play with him while he's available if you do not want a failed objective)
*+ Gwent: Old Pals (you will get a failed objective once some of them are no longer available, so play with them soon enough)
+ Haunted House
+ Hey, You Wanna Look At My Stuff?
+ Hidden Messages of the Nilfgaardian Kind
*! Honor Among Thieves (you must let Rico go during "Ger Junior" main quest to trigger this)
+ Little Red
+ Message from an Old Friend
+ Novigrad Hospitality
+ Novigrad, Closed City
! Now or Never (must be done before going to the Isle of Mists)
+ Of Dairy and Darkness
+ Of Swords and Dumplings
# Out On Your Arse!
+ Race: The Great Erasmus Vegelbud Memorial Derby
*! Reason of State (be careful not to beat up Dijkstra while rescuing Philippa or you will lose this quest even if you completed "A Deadly Plot")
+ Redania's Most Wanted
# Rough Neighbourhood
+ Spooked Mare
# Strangers in the Night
+ The Dwarven Document Dilemma
! The Nobleman Statuette (must be completed before "Now or Never" or before the Battle of Kaer Morhen if you romanced Triss)
! The Soldier Statuette (must be completed before "Now or Never" or before the Battle of Kaer Morhen if you romanced Triss, and you must find a green statuette during "A Dangerous Game")
# Warehouse of Woe
=== SKELLIGE === (work in progress)
A Bard's Beloved
A Hallowed Horn
Abandoned Sawmill
Brave Fools Die Young
! Coronation (must be done before going to the Isle of Mists)
Crime and Punishment
Finders Keepers
+ Fists of Fury: Skellige
Flesh for Sale
For Fame and Glory
*+ Gwent: Skellige Style (make sure to play with Lugos while he's available of you will get a failed objective)
In the Heart of the Woods
In Wolf's Clothing
Iron Maiden
! King's Gambit (must be done before going to the Isle of Mists)
! Lord of Undvik (must be done before going to the Isle of Mists)
Master of the Arena
Peace Disturbed
! Possession (must be done before sailing off for the Sunstone)
+ Practicum in Advanced Alchemy
+ Shock Therapy
Stranger in a Strange Land
Taken as a Lass
The Cave of Dreams
The Family Blade
+ The Heroes' Pursuits: Fayrlund
+ The Heroes' Pursuits: For the Goddess' Glory!
+ The Heroes' Pursuits: Fyresdal
+ The Heroes' Pursuits: Kaer Trolde
! The Last Wish (must be done before going to the Isle of Mists)
! The Lord of Undvik (must be done before going to the Isle of Mists)
The Nithing
+ The Path of Warriors
The Prize of Honor
The Sad Tale of the Grossbart Brothers
+ The Tower Outta Nowhere
Worthy of Trust
=== KAER MORHEN ===
*+ Bastion (requires a magic lamp, so you must have completed "Magic Lamp" first)
+ Berengar's Blade
+ Greenhouse Effect
+ Monster Slayer
+ The Witchers' Forge
