Can large airliners such as a 747 maneuver without electricity?
Flight controls are pretty hard to break

For the 747 (at least through the -400) specifically, the controls are entirely hydromechanical, so yes, they will work without electrical power.  In general, all non-FBW airliners are this way.

FBW airliners vary, though.  All FBW Boeings and the first generation FBW Airbii (A320 family, A330/340) have hydromechanical backups to the FBW system.  The second generation Airbus FBW system, found in the A380 and A350, has abandoned hydromechanical backup controls in favor of independently powered electrical backup systems.

In addition, the chances of total electrical failure are extremely remote -- a failed engine will likely be windmilling (spinning from airflow through it) and thus turning its generator to provide some power, the APU has a generator on it in case all the engines seize up, and there is also a generator that is directly or indirectly powered by the Ram Air Turbine on airliners that use one (all non-reversion twins have one, and so do the A380 and the 747-8 -- earlier 747s don't, relying on windmilling engines for electrical and hydraulic power instead).  Finally, the aircraft has batteries that can provide a limited power reserve if all these other systems fail.  (FBW aircraft add to this with dedicated batteries for at least some parts of the FBW system.)

However, power loss is still a serious emergency

The main hazard posed by a severe electrical power failure, though, is trying to fly around in the clouds with one -- it can render you effectively "no-gyro", especially on older/smaller types that don't have a standby gyroscopic instrument with a dedicated power supply/internal batteries.  There have been cases where small airliners have gone down due to power failures -- while the flight controls were working fine, without power or a visible horizon, the pilots became spatially disoriented, and you can guess the rest.