According to the preliminary report of the Italian authorities, the MD
87 hit the Cessna at 146kts just after takeoff, hit the end of the runway, turned approximately 45% sideways and hit a massive concrete structure aka baggage handling building (which was as long as the MD
87 turned at 45%). The report estimates impact speed at 139kts, causing two of the concrete support pillars to buckle in. Add a fire fueled by 10tons of fuel.
Guess the deceleration forces (139 kts to standstill within a couple of metres...) were too great.