Jim,
Respectfully suggest you read about hibernation on the MS website.
There is no requirement for the system to have any power, as system state is written out to disk. When the system is powered on, the hiberfil.sys is read and the system resumes from that point.
You are right in that most PCs do, in fact, draw a small charge to supply the mobo with enough power to support certain functions - e.g. Wake-on-LAN - but it is not a requirement for Hibernation.
I know this from personal experience - I have put a laptop into hibernation, unplugged it and removed the battery; it still resumed from the point of hibernation when I powered it up again.
Go try it yourself!
SD