I am new to redeeming krisflyer miles and have been searching the ideal itinerary to book my family on a trip to Phuket from Melbourne.

on the outbound trip we want to take advantage of a free stopover in Singapore. There is availability on MEL to SIN leg but after the stopover all flights from SIN to HKT are on waitlist.
The return flights have plenty of availability.

My question is what if the waitlist doesnt clear and we are already in Singapore with a return ticket that origionates from HKT?

appreciate any advice before I redeem.