The Battery could have come disconnected. the switch on the plane may not be going all the way on,, is it mounted in the side of the fuse, and if it was, are you hearing it click when you put it in the on position, if the wood on the plane is restricting the switch from clicking into position it could shut off in flight from the vibrations.

The plane could have been too nose heavy, was there are strong wind blowing? you said you were diving, so if you were diving with the wind hitting the top of your wing and a nose heavy plane, this could have prevented it from climbing out fast enough.

I would say a possible bad crystal but does that even use a crystal?

Sometimes a bad receiver will act that way also, it does happen even new out of the box.

Did the elevator linkage become detached somewhere on the servo or the control horn? did you try ailerons and rudder or shutting down the motor during its fall?? if nothing happened then most likely your power got disconnected somehow.

just a few suggestions out of 5 kabillion things that could have happened with out seeing it or flying it myself,,

But I have been there all tooo many times and I'm sure I'll be there again,, LOL its just part of the hobby.. I just put on a smile and get the glue back out. I hope it was at least a cool crash to see[X(] thats the only entertainment you get out of your plane during a crash for the work of putting it together. By the way what plane was it. ARF / Kit ?? what size 40 / 60 / bigger
Good luck to you.