For Williams, it will come down to a question of legacy over money and boxing.
The 28-year-old has said he wants to be one of the greatest cross-code athletes of all time and winning World Cups in two different codes will help him achieve that. On the flip-side, the off-season is the only time he can fully commit to boxing and he has a New Zealand heavyweight title to defend.
He's expected to return to rugby next year to play for the Chiefs but nothing is ever guaranteed with Williams until it happens.
The Roosters' second-rower is a guaranteed selection if he wants to play for the Kiwis, and his schedule and management team allow it, but there's almost a sense of resignation he won't be available. He would certainly add star power to what is already shaping as a good squad.
"It's one of the strongest squads we have had to pick for quite some time," Kearney said. "The calibre of the guys who miss out says a lot about the quality of this group."
The selectors are likely to plump for a 13 forwards, 11 backs split and will want some second-rowers and back-rowers who can also play either prop or centre. That increases the stocks of players like Greg Eastwood, Frank-Paul Nuuausala, Elijah Taylor and Alex Glenn but Kearney is cautious of picking too many utilities and not enough specialists. He said it happened for this year's Anzac test, although some selections were foisted on the Kiwis because of injuries and unavailability, and had an impact on performance.
The selectors will watch tomorrow's grand final between the Roosters and Sea Eagles with a degree of nervousness because of the large number of Kiwis involved. They so far have close to a full squad to choose from, with only Gerard Beale, Matt Duffie and Benji Marshall unavailable.
Issac Luke is likely to be the only specialist hooker, with Thomas Leuluai and Taylor providing dummy-half cover. Winger Roger Tuivasa-Sheck looms as the only debutant, although hard-running Roosters prop Sam Moa and Sea Eagles second-rower Justin Horo are also in contention.
The Kiwis will gather in Sydney next Saturday before flying out to the UK a couple of days later. They will play a warmup against the Cook Islands in Liverpool on October 21 (NZT) before their opening World Cup match against Samoa on October 28 (NZT).