I assume by "modern" you mean "fly by wire". The description creates an expectation that if "the electronics" go off, the plan can no longer fly and will be out of control (e.g. in a flat spin) until it crashes.
There are multiple levels of redundancy in flight critical avionics, and the degree of automation and "flight envelope protection" degrades in stages as specific pieces of equipment fail.
The Airbus system has 4 stages of electronic control modes ("laws" from "normal" through "alternate", "abnormal" and "direct" modes - basically the plane hands more and more control responsibility over to the pilot as things fail.
In any non-normal mode, it's possible to stall or fly the aircraft unsafely, but there's no expectation that the plane would be "out of control".
Most relevantly to the specific question, there is a 5th "mechanical backup" option, as shown by this description of the Airbus flight laws:
The mechanical backup provides for "temporary control" - it's quite unlikely that this would extend to making a safe landing - it wouldn't be possible to put the wheels down, for example, if there were no operating electronics.
Note that loss of all engines does not mean loss of all electricity - planes have a RAT (Ram Air Turbine) for emergencies - a wind-powered generator that pops out and basically turns the planes forward motion into electrical power.
Also, this argument is relevant for commercial passenger planes - for military aircraft, much greater risks are taken for the sake of speed and maneuverability, and fly by wire planes do fall out of the sky: