Willison has signed with French club Grenoble and will join them in August. The Blues will find him hard to replace next year but the real impact of his departure won't be felt until the year after.
Inevitably, many of the biggest names in New Zealand rugby won't be here in 2016. Super Rugby sides need new stars and often it is men like Willison who suddenly blossom when given their big break. Peripheral now, Willison might be a core player in 2016 - but can he afford to take that risk of waiting to see?
There is a natural ebb and flow to the transfer market now that professionalism is well established. The big clubs know the top players tend to structure their contracts around World Cups. Budgets are manipulated to cater for that so that in any given World Cup year, there is a bigger than usual war chest available to hunt the best. Next year could see the market flooded with one of the biggest crops in years.
The All Blacks are a mature side with several first team players well into their 30s. Some will be preparing for their third World Cup, while for a handful, it will be their fourth. Someone such as Tony Woodcock knows he isn't going to go round again for 2019 but may still have one big offshore contract in him. It's the same for Daniel Carter, Nonu, Conrad Smith and Cory Jane. European clubs would break the bank to land Carter, even when pushing 34.
What these senior All Blacks want to do after the next World Cup, probably even they don't know yet, but Willison wasn't prepared to hang around to see.
"I guess we saw at the last World Cup, there was a trend of players leaving," he says. "That wasn't the main reason I chose to take the offer now [with Grenoble] but it was part of my thinking.
"We [he and his partner] had been thinking about an overseas move when the offer came in. It was a good offer and it felt like the timing was right to go after this campaign."
Willison won't be the only one who decides to move on this year. Already Chiefs wing Asaeli Tikoirotuma has been linked with Harlequins and has said he's probably going to exit.
There will be others such as Alapati Leiua, Jack Lam and Faifili Levave who have all committed to Samoa; they may be tempted elsewhere now that they are no longer All Black-eligible.
At every franchise, there are players who are solid professionals with enough experience and ability to be attractive to European and Japanese clubs. The NZRU can only do so much to protect this group.
The big money has to go to the established stars - the obvious next generation of leading All Blacks, such as Aaron Cruden, Charlie Faumuina, Brodie Retallick, Sam Cane, Piutau and Steven Luatua.
There's not enough money to keep everyone, yet the value of this second tier was highlighted before the last World Cup when Jared Payne, Daniel Bowden and Tio Paulo took offshore offers.
All three were seen as possible future All Blacks had they stayed, leading then coach Graham Henry to say: "It irritates me the guys under the All Black group who have a dream about being an All Black for 25 years and then all of a sudden they get offered $500,000 and bugger off and don't carry on and fulfil the dream."