Have had excellent experiences being rebooked with other airlines at the airport in the past, and would always advocate people go to the airport to sort these problems out.
One of the issues with this particular flight has been the times the further delays were announced; when the additional 7 hour delay was announced at 3:30am local time it wasn’t clear if there would be staff at the airport at this hour.
By the time the additional overnight delay was announced (around 8am local), my wife was quite happy to go with the flow and enjoy a day in Singapore (there are worse places to be stuck).
I did try rebook via phone, but as mentioned elsewhere, only offer was a downgrade to Y.