A quick calculation shows that an aircraft approaching at 200mph will impact that UAV with in excess of 54kJ kinetic energy.
BUT, the $12K 29lb UAV is extremely unlikely to be in the hands of a nutter at Heathrow... That kind of kit is used by the professionals...
The nutter will almost certainly have something like a DJI Phantom, which weighs 1400g - ie 3lb ish...