That's pretty much impossible because planes have ram air turbines to provide emergency power to things like communications and emergency beacons even if the rest of the power system fails catastrophically. Also, even if the electrical system did fail the plane would have been able to glide for quite a long time giving them plenty of opportunity to communicate with somebody and they should still show up on radar during that time so it doesn't really explain how they haven't found even a sign of them since.
If the electrical fault occurred in the right place (which apparently isn't that improbable) literally all communication systems would go down. If the fault has occurred at the connection to the comms system, they'd stop broadcasting. That's the only way they've gone off the radar, and anyone is still alive.
It seems more and more likely now that they have been shot down by some western super (pfft) power that has a history of shooting down planes by mistake.