in which case that is major damage or the engine has departed the aircraft completely
If the engine has departed the airframe, the LAST thing you will notice would be the N2 indication.
I've flown a separation in the sim a few times - it's an interesting exercise as the loss of weight on one side means you are applying opposite airleron to rudder. Of course - that's the sim. In the real world the engine tends to depart under thrust - so goes forward, then up and over - in the process taking the leading edge dvices with it so you lose weight, but also lift....