Whittaker had to withdraw hours before the start of the card due to a twisted bowel and a hernia, which required dual emergency surgeries.
With the bout scratched, Gastelum showed up to the arena wearing a UFC title over his shoulder, claiming he won by default. The title he adorned was that of flyweight champion Henry Cejudo, who was one of many guest fighters in attendance.
There has been no official word on whether a fight to establish an interim title holder in Whittaker's absence will be made.
While earning a shot at the title, Adesanya also added another milestone to his evergrowing list.
He might not have finished Silva how many expected, but he faced - and beat - the greatest middleweight in UFC history - living out a dream.
As he put it immediately after the bout: "For a basketballer, this is like playing against Michael Jordan. This is it for me."
The 29-year-old Kiwi remained unbeaten in MMA with a unanimous decision win over Silva at a sold out Rod Laver Arena, with the two putting on a show in the Brazilian's first ever fight Down Under.
After City Kickboxing teammates Kai Kara-France and Shane Young took decision wins earlier on the card, Adesanya followed suit in a showdown of two wild styles.
The influences Silva has had on Adesanya were clear during the fight, with similarities between the approaches of the two obvious to see.
Adesanya started the fight strong and landed some heavy shots in the first round. Silva came back in the second, but a strong third round was enough for a comfortable Adesanya victory. Silva's durability surprised, as Adesanya couldn't knock him down despite planting some good shots on the Brazilian's chin.
"It was just like fighting anyone else, but there were certain things that he was doing that I have seen so many times, that he has caught other people with, like with his hands down, the bounce, calling me on to the cage with his back against the fence, but not me," Adesanya said. "The energy was cool, it was an honour to share the space with him, I can't describe it. As a kid, as a fan, it was cool, just cool. In the long-term, I am definitely getting the belt next."
The fight was named fight of the night, with both athletes earning a US$50,000 bonus.
