Question: As most crashes are on takeoff and landing, and fire is the real killer, most often. Why not have breakaway wings? That's where the gas is. Let's assume a plane has to make a hard landing..upon touchdown/contact jettison the wings. They serve no purpose at that point and they definitely kill people. Breakaway parts/modules are employed in many arenas, so why not wings?

Answer: 
I can't think of an accident scenario where this might help. If you're hitting the ground hard enough to crash but have survivors, you're looking at an accident like [TK 1951](https://en.m.wikipedia.org/wiki/Turkish_Airlines_Flight_1951), where not only was the wreckage all in pretty much the same area, but it didn't even catch on fire. Aviation fuel is not as volatile as movies make it seem. 

Maybe you are thinking of something like [AF 358](https://en.m.wikipedia.org/wiki/Air_France_Flight_358) which overran the end of the runway and burst into flames? Despite that fire everyone survived, but what if they realised it was going to overrun and jettisoned the wings whilst still on the runway? 

Well the biggest problem to me is how to slow the aircraft down without wings. At higher speeds, the wheel brakes are ineffective without the use of ground spoilers. Without the reverse thrust from the engines you are guaranteeing that the aircraft will be going faster when it leaves the runway, leading to a much higher chance of casualties. 

No piece of engineering is perfect either - what happens when it fails and the wings accidentally detach when everything is going well? What if they are flying in severe turbulence and the sensors detect high G forces and confuses that for a hard landing? Or if it a manual jettison, what if the pilots accidentally pull it, or a suicidal pilot does it while the other is looking the other way? 

There are many other problems too, such as how some aircraft are designed with the gear support in the wings, that some have large fuel tanks in the fuselage, and the extra weight and cost of getting such a system certified. Ultimately this suggestion falls into the same bucket as every other drastic safety idea - in trying to fix a problem that barely exists, it creates a lot more in its place.
The early 310s with "tuna tanks" were designed with exactly this scenario in mind. The idea was that the tanks would keep the fuel as far from the cabin as possible and [shear off](https://www.aopa.org/go-fly/aircraft-and-ownership/aircraft-fact-sheets/cessna-310) in a crash. Cessna abandoned this idea some years later when they incorporated aux tanks into the wings (310L) and then later into the nacelles (310N).

I do not know if data exists to quantify the effectiveness of this design feature.