It would be a tough call on any player who thought he was on his way to the UK but, equally, Williams' talents cannot be ignored. He played a huge role in the Roosters' premiership in his first year back in rugby league after a stint with rugby union and is a player with class, confidence and creativity.
Final squads need to be submitted on October 9, meaning the NZRL would at least be able to investigate making a change.
Earlier in the day, Williams gave no hint of the drama that would unfold when he tweeted: "Wishing the kiwis all the best in their title defence, having my first break since 2008. Looking forward to spending time with fam n friends."
Kearney had taken an expect-the-worst-hope-for-the-best attitude around Williams all season so wasn't surprised by his original decision to skip the tournament.
Jeremy Smith is also missing for personal reasons and centre Shaun Kenny-Dowall is out because of the fractured jaw he suffered in Sunday night's grand final win.
"We had planned for Sonny not coming away," Kearney said. "It was the general feeling I had throughout the year. We were planning that he wasn't going to come and most people were probably thinking that, too.
"It would have been great to have all three of those players [who are unavailable] with the group. They all add something and would have been great assets for the team but I'm really, really pleased with the team. The players who haven't been selected, I think that says a lot about the depth of our squad at the moment. I'm really excited about what we have to work with."
Although the Kiwis selectors were always keen to have Williams on deck for the World Cup, he wasn't seen as their most important player. In fact, he wasn't even in their top two.
Souths hooker Issac Luke is irreplaceable and New Zealand would also not have wanted to do without five-eighth Kieran Foran, who had another excellent season with Manly.
Williams' backflip could have something to do with the fact he wants to leave behind a legacy in sport. He has won a rugby union World Cup, two NRL titles nearly a decade apart, a Super Rugby title and a heavyweight boxing title. A league World Cup would only enhance his standing. He's also played only seven tests for the Kiwis, with his last in 2008, and has never been on the winning side in a black-and-white jersey.
