So we all know that right now Tanith has the small problem of having a Remnant fused to her soul right now. Multiple times in the book it has been said there is no hope, but is that necessarily true? Actually, it would be quite easy to bring her back!
So here it is! How To Bring Tanith Back In Easy Steps!
1) Capture the Remnith and contain her.
Admittedly this will be quite difficult, but if Skul cant do it, nobody can!
2) Drag the Remnith out to meet our good old friend, the Banshee!
Do you know what it is yet?
3) Force the Remnith into the headless horseman's carriage once it has been summoned by the Banshee.
Problem One: SOLVED! The Remnant cant survive in a living body, so would be forced to leave!
4) Capture the escaping Remnant in a Soul Catcher.
Easy enough if you are fully prepared.
5) Put Skulduggery in the carriage to make sure Nye (the carriage's destination) releases the now sort-of dead Tanith back into the world.
We know that Nye is scared of Skulduggery, so sending him along is always a bonus. Plus, Skulduggery is already dead so the horseman's carriage wont affect him!
6) Go to Nye, threaten it with impending doom, and release Tanith! She will regain her life the moment she leaves the lab, thoroughly Remnant free!
See? And you thought it would be impossible :p
An alternate theory would be to use Nye to split the soul of the Remnith back into two separate entities, of course.
EDIT: It was recently pointed out to me that the Remnant just dies and disappears when the host body dies, so ignore Step 4 (I would change it but....... dont wanna :p)