Williams has been playing in Europe since quitting New Zealand rugby after the 2011 Rugby World Cup success.
He had stints with glamour club Toulon before announcing his playing retirement in 2015 and then doing TV work in Europe.
However, midway through last year, Racing 92 convinced him to be part of their wider playing squad alongside old mate Dan Carter and the 35-year-old lock agreed to a short-term contract.
"It's one of those things, when you chuck the game in you think, 'that's me' and you have no desire to get back playing," Williams said at the time.
"Then when the body has the time to recuperate you think, 'well, there are possibilities I can go again."
But his deal with Racing didn't extend to the club allowing him to skip last weekend and return for the McCaw wedding.
It was not unexpected. French clubs are notoriously tough on releasing players for non-Top 14 rugby activity during the season.
French clubs Oyonnax and Toulouse would not even release former All Blacks Piri Weepu and Luke McAlister to play in a tribute match in Toulon last year for late team-mate Jerry Collins.
It's not known if Carter, whose wife Honor is also a former Black Sticks hockey star like McCaw's bride, was invited to last weekend's nupitals and was also prevented from travelling.
Racing 92 did not respond to Herald requests for comment.
