Yes, a ferret willing himself to death (failure to thrive/shelter shock)
after surrender to a shelter is all too common.  The reasons it happens
and tips to avoid it are here:
http://www.ferrets1st.com/articles/sheltershock.htm
 
The treatment for it is here:
http://www.ferrets1st.com/articles/Feeding.htm
 
It takes time to cure.  Lots of time, lots of holding, feeding, holding.
I've had cases last up to 6 months, but most are much better within 3
months, some improve within a month.  I've had ferrets that came in,
already ill with other problems, and the shelter shock was just the
final straw and there was no saving them.
 
You will have to keep the group together, but it may be possible to
introduce them into other play groups, if it's done cautiously.  If
there's any indication that he dislikes or fears a new ferret, remove
him from the play group.  I've had instances where a "new" friend seemed
to give a depressed ferret new interest in living.
 
Debi Christy
www.ferrets1st.com
[Posted in FML issue 5065]