If there was a tech log entry for the A/T system the engineers should have carried out the required tests, for those of you with interest they can be seen on the video here:
https://www.sjap.nl/?s=autothrottle
In any event, a failed A/T should not be a reason to crash, presuming the pilots are " in the loop" and competent to diagnose and apply the appropriate actions, the QRH directs the pilots to the most appropriate actions: Re-engage or Disconnect. Taking actions outside of the manufactures guidance is not advised, however, again we are in the realms of speculation, and in this part of the world when anyone says a "source close to" take it with a very large pinch of salt.