Define "modern". The A-10 is only 38 years old, is still in service and is expected to remain so until at least 2020 (its planned replacement, along with many other current service aircraft including the F-15E, F-16 and F/A-18 is the much-maligned F-35 program). It has redundant hydraulic systems for all major control surfaces, plus a set of drect cable linkages, so even in a fully unpowered glide a true "dead stick" landing is possible. However, this is probably an unfair example as the A-10 was designed in part for extreme survivability in low-altitude combat conditions where the aircraft could encounter practically everything that airplanes and their pilots don't like, from small-arms fire and flak to short-range ground or air missiles and even a well-aimed tank or artillery round.
"Modern" fly-by-wire jets typically have similar redundancy, but with no direct mechanical link from stick to control surfaces, they are at least partially dependent on electrical power for the flight control computer (in addition to the power required for the hydraulic motors). In the case of a total loss of electrical power, you're right, the aircraft would be uncontrollable until one of two things happened; the pilot got one of the electrical sources back online (typically an engine-powered generator), or he gave up and punched out.
One might wonder how much has to go wrong for the generator coupled to each engine turbine and the APU to fail, leaving the pilot with only battery power for the displays (and to attempt maybe one engine restart). The answer is "a lot"; the most likely scenario causing a simultaneous failure of all generation systems is a missile impact, and in that scenario most fighters wouldn't make it back anyway. However, a failure in the power distribution system of the aircraft might be more likely; this system is redundant as well, but there are some necessary bottlenecks, and one or two relatively minor failures in series could conceivably disable a plane mid-flight.