Carnet & Mechanical Failure
 

Is there a way to get the deposit back if your motorcycle breaks down in such a bad way that it isn't economical to have it repaired or shipped back to the country of origin??

Yes.

You see the customs people in the country where the bike is and do their paper work .. in other words have the bike 'imported' into that country .. you'll have to pay them according to their rules .. at whatever value they put on it. So best to demonstrate why it is useable and not worth much, start with some photos at the customs office.

Rules and fees will vary by the country of failure to proceed. Could be cheaper to put it on a truck and take it to the next country..