It is understood that there are not likely to be any more announcements before Christmas but that there could be another as early as next month.
McCaw, who last month marked his 100th test as captain when he took the field against Wales in Cardiff, will almost certainly announce his retirement from the game, and midfielder Nonu is being chased by French club Toulon.
Tew said he believed the other players with undecided futures were "well advanced in their thinking".
"We made it really clear [before the World Cup] in 2011 that one of the learnings from '07 was we had too many distractions," he said.
"We're not going to allow that to happen again and the announcement earlier this week about Steve was part of that strategy. Ultimately these players have to make their own decisions. We can't force a timetable on them."
He added: "We're in pretty good shape. We've known for a long time that there's a group of players likely to leave us at the end of the 2015 World Cup. Hopefully we can see them depart in a nice way. In a way it's one of the last pieces of motivation that might be helpful."
Carter's motivation levels, starting early next month when he joins the Crusaders eager to cement the No10 jersey ahead of the hard-charging Colin Slade, will not be in doubt.
But the 32-year-old did make it clear that he needed a new challenge to look forward to.
"Next year will be my 13th year playing professional rugby in New Zealand," he said. "That's a long time ... I just want to play rugby for as long as I can, basically, and I think it would have been challenging to play in New Zealand post-2015 so that's why I explored my options.
"I was looking for a change and I am confident it will add longevity to my career and I'll be able to play another three, four, five years."
Carter, who will join former Canterbury and Crusaders midfield teammate Casey Laulala at Racing Metro, said he looked hard at the club in 2011 before deciding to re-sign with the NZRU.
He will replace Ireland's Jonathan Sexton as Racing Metro's No10.
Carter's best
Debut v Wales in Hamilton in 2003 (55-3 victory):
"That's the one that sticks in my memory the most. That's when the dream became the reality."
100th v England in London in 2013 (30-22 victory):
"My 100th was a very special moment for me and my family as well."
Second test v British and Irish Lions in Wellington in 2005 (48-18 victory):
"I guess performance-wise that second test against the Lions would be the best game I've played in an All Black jersey."