i have mercedes clk certified dealer destroy mine car engine and they want to put new engine, what should i do?

they had mine clk for repair and run mine car without oil and engine jam and now they admit their fault but i dont know new engine gonna good for transmission or what will happen to mine car value and is their new engine has same vin number or is this all reflect on carfax and it was certified car , should i ask them to gave me new car or same kind of car? or should i go to lawyer?