blimey
the reject/go no go decision is up to the captain at every airline I can think of unless the captain is incapacitated. the copilot does not make the decision and the captain is the one to actually take control of the plane and reject (assuming the copilot was flying the takeoff).
mark654321. while windshear/microburst can cause a plane to crash, it does not ALWAYS cause it to crash (go down and land)>
it depends on the severity of the shear, capability of the plane, capability and skill of the crew.
pretty sure that KPHL has windshear detecting equipment , even beyond the old LLWS alert system, but the much better doppler.