This article is from the the official alt.spleen FAQ, by Andrew Stellman with numerous contributions by others.
Andrew says: NOTE: PLEASE DO NOT SEND ANY MAIL TO ME REQUESTING MEDICAL ADVICE! I AM NOT A DOCTOR, AND WILL NOT GIVE YOU ANY USEFUL INFORMATION.
Due to the fact that so many of the higher functions of the body are carried out by the spleen, the entire nervous system will go into shock if the spleen is unconscious for more then ten minutes. The spleen itself will remain relatively unharmed, since it is mostly self-contained. However, without its host body, it will not get the sustenance required to maintain such a high amount of mental activity and, as a result, will die in days.