Well, there is a mod that makes it so you don't die instantly from vital organs being destroyed. It'll give you a short window, so it is rather realistic in that respect. I observed it when I destroyed a spider's heart. Took a few minutes. So you'd have to be quick.
Anyhow, I'mma hunt down a link for you. Now you can be a bit more focused on helping this wonderful modder out, if you possibly can. :D

http://gtm.steamproxy.vip/sharedfiles/filedetails/?id=1076757664
Here is the link.
It is called Death Rattle.

Hi, Brambor! That would be awesome! Rimworld uses mainly two forms of coding: XML and C#. I need help with C#. If you are new to modding I would recommend you to take a look at the Rimworld wiki, there is guides for modding on there. You can also download other peoples mods on github to see how they have done it.

As Fanciful Spoon said, death ratte removes the insta dying.

Fanciful Spoon I have to look into that mod but I think it will be missing real organ failure. I would like to add really complex illnesses related to organ failure, each organ would give you different time window and when your kidneys gets destroyed other organs would suffer from low blood filtration and could be damaged before the person dies so multiple organs would be needed to be given to one person if absence of kidneys are ignored for a day or more.

Smuffle I will look into that and I would like to get access to your code so that I know what have you done and it should help me with poting at parts of code where should I be looking for butchering, organs and such.

Ill upload my code somewhere a bit later. What you should try while adding to this mod is to make surgery available on corpses. If that is done, most problems with my mod will disappear.

That might be quite complicated. Haven't yet looked into it but I thing that surgery is something that is possible only on colonists and that dead bodies are completly different. I might be wrong and therefore I will make myself certain.
What I thought I will try to do is: harvest for organs would try for each organ to be harvested and give all organs which succeded. Or, probably what you ment, choose which organ you want to harvest.
Possibly at your table (your harvesting station) there would be 'harvest heart' and that would accept all corpses with heart. If successful it would give you theirs heart and rest of the body. So if they suffer from artilery blokade or something, the heart should have that as well.

Brambor, as you are saying by harvesting each organ with a success-chance, that is basically surgery. Thus, surgery on corpses would fix most problems. But yeah, I imagine it will be difficult as I suspect corpses are treated like advanced items, not pawns.

The harvesting station, most likely autopsy table, should you succeed, will as you say function like a medical bed, allowing for operations of individual-spesific organs, such as a heart, or a damaged heart even.