thanks everyone, this has been really helpful. mostly likely going to book:
YYZ-xHKG-DPS-xHKG-CAN-xHKG-AKL-xSYD-MEL-xDOH-NYC then 10 month break to use remaining NA segments before -YYZ.

Look reasonable? What would happen if I failed to take the final YYZ flight, is the advice the typical 'don't do it too often and you should be fine'?