A very lucky escape indeed as such accidents are usually fatal if the aurcraft wasn't fully under control until impact.
The aircraft was built in 1971 and contrary to what other reports state it is not a Chancellor for this one has tip tanks.
In 1971 I was a ME demo pilot for Cessna in Europe and that included flying and demonstrating all of the Cessna twins, including SErate of climb. The 411 was the first of the cabin class Cessnas and had a much smaller fin and rudder, big drag producing cowl flaps. Therefore that comment is irrelevant.
The 414 was much like the 401 but pressurised and had 310 hp engines. The original Cessna Owners Manual only shows take off with flaps UP. It does not have a GAMA format POH. The electrical undercarriage system is slow to fully retract and for the gear doors to close. If you do retract the gear at low speeds then the opening main gear doors produce drag and loss of lift and the C of G moves aft as the nose wheel retracts aft and this can affect the VMC.
This aircraft had the RAM modifications with probably 325hp and a Micro VG kit designed to lower the take off safety speed and best SE rate of climb speed. I do not know if RAM or the VG people have published any FAA approved takeoff or climb performance charts using flaps up or 10 for take off and climb. Heresay and visual observations and actual handing characteristics are one thing but testing to an approved schedule is another.
The Cessna 414 is a very nice flying aircraft provided it is not overloaded with equipment. I do not know the history of this aircraft but many that came to Europe at that time were very well equipped with all of the options. They had to be to keep raise the empty weight above 2000kg for if it was below then you had to pay higher import duty.
I have log books full of very happy memories in operating these turbocharged Cessna twins from the Arctic to the Sudan and Saudi Arabia in ISA + 25 and we are currently ISA +15 but that does make a difference in performance.
Let's not speculate on what happened and hope that the co-pilot makes a fully and speedy recovery. The AAIB will certainly be interested in receiving balanced comments from qualified witnesses and any videos that can add value to their investigation.