The 35-year-old Stokes called time on his international career after the final Test against New Zealand last month saying he "didn't have any fight left" after four years of captaining England in the longest format.
It has been suggested that Stokes and previous red-ball coach Brendon McCullum had fallen out and Key believes "anything is possible" now that England have installed Stephen Fleming as the Test mentor.
"It would be a brilliant story if he does," Key told Sky Sports News. "He hasn't (indicated a change of heart), but I wouldn't be surprised. Anything is possible with Ben."
Fleming had worked with Stokes before when coaching Indian Premier League (IPL) sides Chennai Super Kings and Rising Pune Super Giants and could yet persuade the allrounder to reverse his decision.
Stokes also backed his deputy Harry Brook to succeed him as England's Test skipper but Key has decided that Joe Root will return to lead the team.
Brook is already England skipper in both white-ball formats and Key said Fleming endorsed the decision to give the Root the captaincy in Test cricket, having held the position permanently before Stokes.
"He's still developing as a player and as a person, to be honest," Key said of Brook. "The Test match captaincy is the biggest job in cricket in England, and I think that it's perfect now with Joe who gets the chance to do it where he can now take this ship forward as the most senior player by a long, long way.
"Harry can now continue on the project he's done in the white-ball job and continue learning how to become an outstanding leader of a cricket team. You've got the 2027 World Cup, all of those things, and at some stage Harry Brook will be an outstanding Test captain of England cricket. I just didn't feel the time was right now."
Joe Root has made it known that he accepted the England Test captaincy because he wanted to work with new coach Stephen Fleming to "build something pretty special together".
The England and Wales Cricket Board has appointed Stephen Fleming as the England Test Head Coach, while veteran Joe Root has been named captain.
Justin Langer has confirmed that he has not yet been approached or had any talks with anyone for the role of England Test coach.
Cricket Australia is exploring new ways to strengthen its footprint in India, with chief executive Todd Greenberg suggesting the country could even host a Test match between Australia and England.
