Engine Gone

Sounds fishy to me. Have you been to this mechanic before? If the engine turns over and won't fire, is there a spark? Perhaps the camshaft broke, but there would be some bad noises I would think. Somehow this seems like a sham and I would want the car immediately to take somewhere else for a second opinion. I am assuming that you experienced no problems and it ran fine until one day it would not start. Likely a spark problem or fuel problem I would guess.

run a compresion check. If the timing chain breaks you can brake a valve or piston, causing these symptons

Had this happen to me on a Honda. Snapped timing belt engine turned over quickly with no throaty sound. Zinnnng...

Get timing belt/chain checked. Hope the engine is not an "interference engine" = piston whacks valves when engine turns over and valves don't reciprocate.

good luck...