A Matter of Life and Death, is one of the most important quests featured in the second act of the RPG known as Witcher 2 Assassins of Kings Enhanced Edition, but it can be completed only if you side with Iorveth at the end of the first act.
A Matter of Life and Death begins as soon as you complete The War Council quest, and after Saskia is poisoned.
In fact, A Matter of Life and Death is a quest focused on Geralts attempt to save Saskia, by finding the ingredients needed to create a cure.
In other words, A Matter of Life and Death is a short quest, but it is directly linked to other main-quests included in the second act.
Therefore, to complete A Matter of Life and Death, in Witcher 2, the following quests must be played as well: Royal Blood, Subterranean Life, Hunting Magic and Where is Triss Merigold?.
Only if you advance in these quests, you will be able to advance through the games story and save Saskia.
“As you already know, Saskia, known to those who loved her as the Virgin of Aedirn and to those close to King Henselt as The Insolent Wench had been poisoned. There are numerous stories about how the witcher cured the girl, how he climbed a glass mountain and placed a healing kiss on her carmine lips. Well, none of those are true.
Several unusual ingredients were needed to prepare the antidote that is a rose of remembrance, a dragons dream, an immortelle and royal blood. The witcher began his search for these ingredients.”
When to start
It is important to know that completing A Matter of Life and Death allows you to unlock the final quests of the second chapter, therefore, it is a good idea to complete all side-quests and main quests unrelated to this one.
Note: Remember that, Hatred Symbolized is a quest which can be completed only if you take the sword from Saskia, which means that you will have the chance to get the item, only if you cure her.
If you managed to collect all items for the cure, by solving the quests mentioned above, it is time to continue A Matter of Life and Death.
Find Philippa in Vergen and give her the ingredients, then watch the cutscene showing the sorceress performing the ritual on the Virgin of Aedirn.
Talk to Saskia and tell her that you have your own reasons to help her, and then A Matter of Life and Death, and Hatred Symbolized will end.
Note: The next quest in line is The Eternal Battle. Even if you have only two artifacts needed to lift the mist from the battlefield, remember that Philippa promised to help you by finding the rest. Explore Saskias house for additional money, then head back to Philippa.