In Windows 7 there's a hybrid sleep mode, in which the contents of memory is saved on disk and maintained in RAM as well.
My question is can I be absolutely sure that nothing will go wrong when I cut off the power from the computer that is in hybrid sleep state?
Yes, to the extent that hibernation is stable enough for your requirements.
According to microsoft, your session is protected from loss by power outage while in hybrid-sleep, because the entirety of your user-space RAM image is copied to your hard disk (in the hiberfil.sys file), so long as your system retains the session, then upon boot, it will load it from disk, as though you had never slept.
To enable hybrid-sleep (which is primarily designed for desktops), you must enable the feature. Then use the normal sleep gestures to activate sleep, and the system will enter a low-power mode.
